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• New CentOS/cPanel servers showing high load averages at idle

  - by Jax

  I have taken delivery of two identically specced CentOS/cPanel servers, showing the same behaviour of a resting load average of 1.30, 1.21, 1.16 and yet the CPU is sitting 100% idle. Hardware: Xeon(R) CPU E3-1270 4GB RAM Behavior:- top shows CPU 99.9% idle virtually no disk IO Some command output :- uname -a Linux server.myserver.com 2.6.18-308.4.1.el5PAE #1 SMP Tue Apr 17 17:47:38 EDT 2012 i686 i686 i386 GNU/Linux top top - 10:37:50 up 1:47, 1 user, load average: 1.28, 1.20, 1.17 Tasks: 199 total, 1 running, 198 sleeping, 0 stopped, 0 zombie Cpu(s): 0.0%us, 0.0%sy, 0.0%ni, 99.9%id, 0.1%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 4125104k total, 438764k used, 3686340k free, 25788k buffers Swap: 2096440k total, 0k used, 2096440k free, 291080k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 1 root 15 0 2160 640 552 S 0.0 0.0 0:00.89 init 2 root RT -5 0 0 0 S 0.0 0.0 0:00.00 migration/0 3 root 34 19 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/0 4 root RT -5 0 0 0 S 0.0 0.0 0:00.00 watchdog/0 5 root RT -5 0 0 0 S 0.0 0.0 0:00.00 migration/1 6 root 34 19 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/1 7 root RT -5 0 0 0 S 0.0 0.0 0:00.00 watchdog/1 8 root RT -5 0 0 0 S 0.0 0.0 0:00.00 migration/2 9 root 35 19 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/2 10 root RT -5 0 0 0 S 0.0 0.0 0:00.00 watchdog/2 11 root RT -5 0 0 0 S 0.0 0.0 0:00.00 migration/3 12 root 34 19 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/3 13 root RT -5 0 0 0 S 0.0 0.0 0:00.00 watchdog/3 14 root RT -5 0 0 0 S 0.0 0.0 0:00.00 migration/4 15 root 34 19 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/4 16 root RT -5 0 0 0 S 0.0 0.0 0:00.00 watchdog/4 17 root RT -5 0 0 0 S 0.0 0.0 0:00.00 migration/5 18 root 38 19 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/5 19 root RT -5 0 0 0 S 0.0 0.0 0:00.00 watchdog/5 20 root RT -5 0 0 0 S 0.0 0.0 0:00.00 migration/6 21 root 34 19 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/6 22 root RT -5 0 0 0 S 0.0 0.0 0:00.00 watchdog/6 23 root RT -5 0 0 0 S 0.0 0.0 0:00.00 migration/7 24 root 34 19 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/7 25 root RT -5 0 0 0 S 0.0 0.0 0:00.00 watchdog/7 26 root 10 -5 0 0 0 S 0.0 0.0 0:06.42 events/0 27 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 events/1 28 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 events/2 29 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 events/3 30 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 events/4 31 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 events/5 32 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 events/6 33 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 events/7 34 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 khelper 35 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 kthread 45 root 13 -5 0 0 0 S 0.0 0.0 0:00.00 kblockd/0 46 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 kblockd/1 47 root 14 -5 0 0 0 S 0.0 0.0 0:00.00 kblockd/2 48 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 kblockd/3 49 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 kblockd/4 50 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 kblockd/5 51 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 kblockd/6 52 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 kblockd/7 53 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 kacpid 189 root 11 -5 0 0 0 S 0.0 0.0 0:00.00 cqueue/0 190 root 11 -5 0 0 0 S 0.0 0.0 0:00.00 cqueue/1 191 root 12 -5 0 0 0 S 0.0 0.0 0:00.00 cqueue/2 192 root 12 -5 0 0 0 S 0.0 0.0 0:00.00 cqueue/3 193 root 13 -5 0 0 0 S 0.0 0.0 0:00.00 cqueue/4 194 root 13 -5 0 0 0 S 0.0 0.0 0:00.00 cqueue/5 195 root 14 -5 0 0 0 S 0.0 0.0 0:00.00 cqueue/6 196 root 14 -5 0 0 0 S 0.0 0.0 0:00.00 cqueue/7 199 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 khubd ps axf PID TTY STAT TIME COMMAND 1 ? Ss 0:00 init [3] 2 ? S< 0:00 [migration/0] 3 ? SN 0:00 [ksoftirqd/0] 4 ? S< 0:00 [watchdog/0] 5 ? S< 0:00 [migration/1] 6 ? SN 0:00 [ksoftirqd/1] 7 ? S< 0:00 [watchdog/1] 8 ? S< 0:00 [migration/2] 9 ? SN 0:00 [ksoftirqd/2] 10 ? S< 0:00 [watchdog/2] 11 ? S< 0:00 [migration/3] 12 ? SN 0:00 [ksoftirqd/3] 13 ? S< 0:00 [watchdog/3] 14 ? S< 0:00 [migration/4] 15 ? SN 0:00 [ksoftirqd/4] 16 ? S< 0:00 [watchdog/4] 17 ? S< 0:00 [migration/5] 18 ? SN 0:00 [ksoftirqd/5] 19 ? S< 0:00 [watchdog/5] 20 ? S< 0:00 [migration/6] 21 ? SN 0:00 [ksoftirqd/6] 22 ? S< 0:00 [watchdog/6] 23 ? S< 0:00 [migration/7] 24 ? SN 0:00 [ksoftirqd/7] 25 ? S< 0:00 [watchdog/7] 26 ? S< 0:06 [events/0] 27 ? S< 0:00 [events/1] 28 ? S< 0:00 [events/2] 29 ? S< 0:00 [events/3] 30 ? S< 0:00 [events/4] 31 ? S< 0:00 [events/5] 32 ? S< 0:00 [events/6] 33 ? S< 0:00 [events/7] 34 ? S< 0:00 [khelper] 35 ? S< 0:00 [kthread] 45 ? S< 0:00 \_ [kblockd/0] 46 ? S< 0:00 \_ [kblockd/1] 47 ? S< 0:00 \_ [kblockd/2] 48 ? S< 0:00 \_ [kblockd/3] 49 ? S< 0:00 \_ [kblockd/4] 50 ? S< 0:00 \_ [kblockd/5] 51 ? S< 0:00 \_ [kblockd/6] 52 ? S< 0:00 \_ [kblockd/7] 53 ? S< 0:00 \_ [kacpid] 189 ? S< 0:00 \_ [cqueue/0] 190 ? S< 0:00 \_ [cqueue/1] 191 ? S< 0:00 \_ [cqueue/2] 192 ? S< 0:00 \_ [cqueue/3] 193 ? S< 0:00 \_ [cqueue/4] 194 ? S< 0:00 \_ [cqueue/5] 195 ? S< 0:00 \_ [cqueue/6] 196 ? S< 0:00 \_ [cqueue/7] 199 ? S< 0:00 \_ [khubd] 201 ? S< 0:00 \_ [kseriod] 301 ? S 0:00 \_ [khungtaskd] 302 ? S 0:00 \_ [pdflush] 303 ? S 0:00 \_ [pdflush] 304 ? S< 0:00 \_ [kswapd0] 305 ? S< 0:00 \_ [aio/0] 306 ? S< 0:00 \_ [aio/1] 307 ? S< 0:00 \_ [aio/2] 308 ? S< 0:00 \_ [aio/3] 309 ? S< 0:00 \_ [aio/4] 310 ? S< 0:00 \_ [aio/5] 311 ? S< 0:00 \_ [aio/6] 312 ? S< 0:00 \_ [aio/7] 472 ? S< 0:00 \_ [kpsmoused] 551 ? S< 0:00 \_ [ata/0] 552 ? S< 0:00 \_ [ata/1] 553 ? S< 0:00 \_ [ata/2] 554 ? S< 0:00 \_ [ata/3] 555 ? S< 0:00 \_ [ata/4] 556 ? S< 0:00 \_ [ata/5] 557 ? S< 0:00 \_ [ata/6] 558 ? S< 0:00 \_ [ata/7] 559 ? S< 0:00 \_ [ata_aux] 569 ? S< 0:00 \_ [scsi_eh_0] 570 ? S< 0:00 \_ [scsi_eh_1] 571 ? S< 0:00 \_ [scsi_eh_2] 572 ? S< 0:00 \_ [scsi_eh_3] 573 ? S< 0:00 \_ [scsi_eh_4] 574 ? S< 0:00 \_ [scsi_eh_5] 593 ? S< 0:00 \_ [kstriped] 630 ? S< 0:00 \_ [kjournald] 655 ? S< 0:00 \_ [kauditd] 1860 ? S< 0:00 \_ [kmpathd/0] 1861 ? S< 0:00 \_ [kmpathd/1] 1862 ? S< 0:00 \_ [kmpathd/2] 1863 ? S< 0:00 \_ [kmpathd/3] 1864 ? S< 0:00 \_ [kmpathd/4] 1865 ? S< 0:00 \_ [kmpathd/5] 1866 ? S< 0:00 \_ [kmpathd/6] 1867 ? S< 0:00 \_ [kmpathd/7] 1868 ? S< 0:00 \_ [kmpath_handlerd] 1902 ? S< 0:00 \_ [kjournald] 1904 ? S< 0:00 \_ [kjournald] 1906 ? S< 0:00 \_ [kjournald] 1908 ? S< 0:00 \_ [kjournald] 1910 ? S< 0:00 \_ [kjournald] 2184 ? S< 0:00 \_ [iscsi_eh] 2288 ? S< 0:00 \_ [cnic_wq] 2298 ? S< 0:00 \_ [bnx2i_thread/0] 2299 ? S< 0:00 \_ [bnx2i_thread/1] 2300 ? S< 0:00 \_ [bnx2i_thread/2] 2301 ? S< 0:00 \_ [bnx2i_thread/3] 2302 ? S< 0:00 \_ [bnx2i_thread/4] 2303 ? S< 0:00 \_ [bnx2i_thread/5] 2304 ? S< 0:00 \_ [bnx2i_thread/6] 2305 ? S< 0:00 \_ [bnx2i_thread/7] 2330 ? S< 0:00 \_ [ib_addr] 2359 ? S< 0:00 \_ [ib_mcast] 2360 ? S< 0:00 \_ [ib_inform] 2361 ? S< 0:00 \_ [local_sa] 2371 ? S< 0:00 \_ [iw_cm_wq] 2381 ? S< 0:00 \_ [ib_cm/0] 2382 ? S< 0:00 \_ [ib_cm/1] 2383 ? S< 0:00 \_ [ib_cm/2] 2384 ? S< 0:00 \_ [ib_cm/3] 2385 ? S< 0:00 \_ [ib_cm/4] 2386 ? S< 0:00 \_ [ib_cm/5] 2387 ? S< 0:00 \_ [ib_cm/6] 2388 ? S< 0:00 \_ [ib_cm/7] 2398 ? S< 0:00 \_ [rdma_cm] 2684 ? S< 0:00 \_ [bond0] 2882 ? S< 0:00 \_ [bond1] 3195 ? S< 0:00 \_ [kondemand/0] 3197 ? S< 0:00 \_ [kondemand/1] 3198 ? S< 0:00 \_ [kondemand/2] 3199 ? S< 0:00 \_ [kondemand/3] 3200 ? S< 0:00 \_ [kondemand/4] 3201 ? S< 0:00 \_ [kondemand/5] 3202 ? S< 0:00 \_ [kondemand/6] 3203 ? S< 0:00 \_ [kondemand/7] 688 ? S<s 0:00 /sbin/udevd -d 2425 ? S<Lsl 0:00 iscsiuio 2432 ? Ss 0:00 iscsid 2434 ? S<Ls 0:00 iscsid 3061 ? S<sl 0:00 auditd 3063 ? S<sl 0:00 \_ /sbin/audispd 3121 ? Ss 0:00 syslogd -m 0 3124 ? Ss 0:00 klogd -x 3220 ? Ss 0:00 irqbalance 3278 ? Ss 0:00 dbus-daemon --system 3324 ? Ss 0:00 /usr/sbin/acpid 3337 ? Ss 0:00 hald 3338 ? S 0:00 \_ hald-runner 3345 ? S 0:00 \_ hald-addon-acpi: listening on acpid socket /var/run/acpid.socket 3349 ? S 0:00 \_ hald-addon-keyboard: listening on /dev/input/event1 3360 ? S 0:00 \_ hald-addon-storage: polling /dev/sr0 3413 ? Ssl 0:00 automount 3435 ? Ssl 0:00 /usr/sbin/named -u named 3466 ? Ss 0:00 /usr/sbin/sshd 4072 ? Ss 0:00 \_ sshd: root@pts/0 4078 pts/0 Ss 0:00 \_ -bash 5436 pts/0 R+ 0:00 \_ ps axf 3484 ? Ss 0:00 xinetd -stayalive -pidfile /var/run/xinetd.pid 3500 ? SLs 0:00 ntpd -u ntp:ntp -p /var/run/ntpd.pid -g 3514 ? S 0:00 /bin/sh /usr/bin/mysqld_safe --datadir=/var/lib/mysql --pid-file=/var/lib/mysql/server.myserver.com.pid 3575 ? Sl 0:00 \_ /usr/sbin/mysqld --basedir=/ --datadir=/var/lib/mysql --user=mysql --log-error=/var/lib/mysql/server.myserver.com.err --pid-fil 3687 ? Ss 0:00 /usr/sbin/exim -bd -q1h 3709 ? Ss 0:00 /usr/sbin/dovecot 3710 ? S 0:00 \_ dovecot-auth 3725 ? S 0:00 \_ pop3-login 3726 ? S 0:00 \_ pop3-login 3727 ? S 0:00 \_ imap-login 3728 ? S 0:00 \_ imap-login 3729 ? Ss 0:00 /usr/local/apache/bin/httpd -k start -DSSL 4326 ? S 0:00 \_ /usr/bin/perl /usr/local/cpanel/bin/leechprotect 4332 ? S 0:00 \_ /usr/local/apache/bin/httpd -k start -DSSL 4333 ? S 0:00 \_ /usr/local/apache/bin/httpd -k start -DSSL 4334 ? S 0:00 \_ /usr/local/apache/bin/httpd -k start -DSSL 4335 ? S 0:00 \_ /usr/local/apache/bin/httpd -k start -DSSL 4336 ? S 0:00 \_ /usr/local/apache/bin/httpd -k start -DSSL 4337 ? S 0:00 \_ /usr/local/apache/bin/httpd -k start -DSSL 4382 ? S 0:00 \_ /usr/local/apache/bin/httpd -k start -DSSL 4383 ? S 0:00 \_ /usr/local/apache/bin/httpd -k start -DSSL 4384 ? S 0:00 \_ /usr/local/apache/bin/httpd -k start -DSSL 5389 ? S 0:00 \_ /usr/local/apache/bin/httpd -k start -DSSL 5390 ? S 0:00 \_ /usr/local/apache/bin/httpd -k start -DSSL 3741 ? Ss 0:00 pure-ftpd (SERVER) 3746 ? S 0:00 /usr/sbin/pure-authd -s /var/run/ftpd.sock -r /usr/sbin/pureauth 3759 ? Ss 0:00 crond 3772 ? Ss 0:00 /usr/sbin/atd 3909 ? S 0:00 cpsrvd (SSL) - waiting for connections 5435 ? Z 0:00 \_ [cpsrvd-ssl] <defunct> 3931 ? S 0:00 queueprocd - wait to process a task 3948 ? S 0:00 tailwatchd 3954 ? SN 0:00 cpanellogd - sleeping for logs 4003 ? Ss 0:00 ./nimbus /opt/nimsoft 4016 ? S 0:00 \_ nimbus(controller) 4053 ? Sl 0:00 \_ nimbus(spooler) 4066 ? S 0:00 \_ nimbus(hdb) 4069 ? S 0:00 \_ nimbus(cdm) 4070 ? S 0:00 \_ nimbus(processes) 4023 ? S 0:00 /usr/sbin/smartd -q never 4027 tty1 Ss+ 0:00 /sbin/mingetty tty1 4028 tty2 Ss+ 0:00 /sbin/mingetty tty2 4029 tty3 Ss+ 0:00 /sbin/mingetty tty3 4030 tty4 Ss+ 0:00 /sbin/mingetty tty4 4031 tty5 Ss+ 0:00 /sbin/mingetty tty5 4033 tty6 Ss+ 0:00 /sbin/mingetty tty6 4035 ttyS1 Ss+ 0:00 /sbin/agetty -h -L ttyS1 19200 vt100 vmstat 10 6 procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------ r b swpd free buff cache si so bi bo in cs us sy id wa st 0 0 0 3718136 25684 257424 0 0 8 3 127 189 0 0 100 0 0 0 0 0 3718136 25700 257420 0 0 0 7 1013 1500 0 0 100 0 0 0 0 0 3718136 25700 257424 0 0 0 1 1013 1551 0 0 100 0 0 0 0 0 3718136 25700 257424 0 0 0 0 1012 1469 0 0 100 0 0 1 0 0 3712680 25716 257424 0 0 0 2 1013 1542 0 0 100 0 0 0 0 0 3718376 25740 257424 0 0 0 46 1017 1534 0 0 100 0 0 Can anyone advise me as to what is the cause of and how I may resolve this behaviour? A kernel/driver conflict perhaps? I don't see any processes in R or D state that might inflate the load averages artificially, I realise it may be considered low in an 8 thread system but its higher at idle than any normal behaviour I've previously come across. Thanks in advance for your time. Edit: iotop Total DISK READ: 0.00 B/s | Total DISK WRITE: 0.00 B/s TID PRIO USER DISK READ DISK WRITE SWAPIN IO> COMMAND 26 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.29 % [events/0] 3205 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.10 % [kondemand/2] 3208 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kondemand/5] 3209 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kondemand/6] 3207 be/3 root 0.00 B/s 0.00 B/s 0.10 % 0.00 % [kondemand/4] 3210 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kondemand/7] 3227 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % irqbalance 3288 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [rpciod/1] 3287 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [rpciod/0] 3206 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kondemand/3] 3069 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % auditd 3070 be/2 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % audispd 655 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kauditd] 3619 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % automount 3 be/7 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [ksoftirqd/0] 3068 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % auditd 29 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [events/3] 4 rt/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [watchdog/0] 7 rt/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [watchdog/1] 10 rt/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [watchdog/2] 13 rt/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [watchdog/3] 16 rt/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [watchdog/4] 19 rt/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [watchdog/5] 22 rt/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [watchdog/6] 25 rt/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [watchdog/7] 27 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [events/1] 28 be/3 root 0.00 B/s 0.00 B/s 0.29 % 0.00 % [events/2] 30 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [events/4] 31 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [events/5] 32 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [events/6] 33 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [events/7] 34 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [khelper] 35 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kthread] 45 be/3 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kblockd/0]

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• Very different I/O performance in C++ on Windows

  - by Mr.Gate

  Hi all, I'm a new user and my english is not so good so I hope to be clear. We're facing a performance problem using large files (1GB or more) expecially (as it seems) when you try to grow them in size. Anyway... to verify our sensations we tryed the following (on Win 7 64Bit, 4core, 8GB Ram, 32 bit code compiled with VC2008) a) Open an unexisting file. Write it from the beginning up to 1Gb in 1Mb slots. Now you have a 1Gb file. Now randomize 10000 positions within that file, seek to that position and write 50 bytes in each position, no matter what you write. Close the file and look at the results. Time to create the file is quite fast (about 0.3"), time to write 10000 times is fast all the same (about 0.03"). Very good, this is the beginnig. Now try something else... b) Open an unexisting file, seek to 1Gb-1byte and write just 1 byte. Now you have another 1Gb file. Follow the next steps exactly same way of case 'a', close the file and look at the results. Time to create the file is the faster you can imagine (about 0.00009") but write time is something you can't believe.... about 90"!!!!! b.1) Open an unexisting file, don't write any byte. Act as before, ramdomizing, seeking and writing, close the file and look at the result. Time to write is long all the same: about 90"!!!!! Ok... this is quite amazing. But there's more! c) Open again the file you crated in case 'a', don't truncate it... randomize again 10000 positions and act as before. You're fast as before, about 0,03" to write 10000 times. This sounds Ok... try another step. d) Now open the file you created in case 'b', don't truncate it... randomize again 10000 positions and act as before. You're slow again and again, but the time is reduced to... 45"!! Maybe, trying again, the time will reduce. I actually wonder why... Any Idea? The following is part of the code I used to test what I told in previuos cases (you'll have to change someting in order to have a clean compilation, I just cut & paste from some source code, sorry). The sample can read and write, in random, ordered or reverse ordered mode, but write only in random order is the clearest test. We tryed using std::fstream but also using directly CreateFile(), WriteFile() and so on the results are the same (even if std::fstream is actually a little slower). Parameters for case 'a' = -f_tempdir_\casea.dat -n10000 -t -p -w Parameters for case 'b' = -f_tempdir_\caseb.dat -n10000 -t -v -w Parameters for case 'b.1' = -f_tempdir_\caseb.dat -n10000 -t -w Parameters for case 'c' = -f_tempdir_\casea.dat -n10000 -w Parameters for case 'd' = -f_tempdir_\caseb.dat -n10000 -w Run the test (and even others) and see... // iotest.cpp : Defines the entry point for the console application. // #include <windows.h> #include <iostream> #include <set> #include <vector> #include "stdafx.h" double RealTime_Microsecs() { LARGE_INTEGER fr = {0, 0}; LARGE_INTEGER ti = {0, 0}; double time = 0.0; QueryPerformanceCounter(&ti); QueryPerformanceFrequency(&fr); time = (double) ti.QuadPart / (double) fr.QuadPart; return time; } int main(int argc, char* argv[]) { std::string sFileName ; size_t stSize, stTimes, stBytes ; int retval = 0 ; char *p = NULL ; char *pPattern = NULL ; char *pReadBuf = NULL ; try { // Default stSize = 1<<30 ; // 1Gb stTimes = 1000 ; stBytes = 50 ; bool bTruncate = false ; bool bPre = false ; bool bPreFast = false ; bool bOrdered = false ; bool bReverse = false ; bool bWriteOnly = false ; // Comsumo i parametri for(int index=1; index < argc; ++index) { if ( '-' != argv[index][0] ) throw ; switch(argv[index][1]) { case 'f': sFileName = argv[index]+2 ; break ; case 's': stSize = xw::str::strtol(argv[index]+2) ; break ; case 'n': stTimes = xw::str::strtol(argv[index]+2) ; break ; case 'b':stBytes = xw::str::strtol(argv[index]+2) ; break ; case 't': bTruncate = true ; break ; case 'p' : bPre = true, bPreFast = false ; break ; case 'v' : bPreFast = true, bPre = false ; break ; case 'o' : bOrdered = true, bReverse = false ; break ; case 'r' : bReverse = true, bOrdered = false ; break ; case 'w' : bWriteOnly = true ; break ; default: throw ; break ; } } if ( sFileName.empty() ) { std::cout << "Usage: -f<File Name> -s<File Size> -n<Number of Reads and Writes> -b<Bytes per Read and Write> -t -p -v -o -r -w" << std::endl ; std::cout << "-t truncates the file, -p pre load the file, -v pre load 'veloce', -o writes in order mode, -r write in reverse order mode, -w Write Only" << std::endl ; std::cout << "Default: 1Gb, 1000 times, 50 bytes" << std::endl ; throw ; } if ( !stSize || !stTimes || !stBytes ) { std::cout << "Invalid Parameters" << std::endl ; return -1 ; } size_t stBestSize = 0x00100000 ; std::fstream fFile ; fFile.open(sFileName.c_str(), std::ios_base::binary|std::ios_base::out|std::ios_base::in|(bTruncate?std::ios_base::trunc:0)) ; p = new char[stBestSize] ; pPattern = new char[stBytes] ; pReadBuf = new char[stBytes] ; memset(p, 0, stBestSize) ; memset(pPattern, (int)(stBytes&0x000000ff), stBytes) ; double dTime = RealTime_Microsecs() ; size_t stCopySize, stSizeToCopy = stSize ; if ( bPre ) { do { stCopySize = std::min(stSizeToCopy, stBestSize) ; fFile.write(p, stCopySize) ; stSizeToCopy -= stCopySize ; } while (stSizeToCopy) ; std::cout << "Creating time is: " << xw::str::itoa(RealTime_Microsecs()-dTime, 5, 'f') << std::endl ; } else if ( bPreFast ) { fFile.seekp(stSize-1) ; fFile.write(p, 1) ; std::cout << "Creating Fast time is: " << xw::str::itoa(RealTime_Microsecs()-dTime, 5, 'f') << std::endl ; } size_t stPos ; ::srand((unsigned int)dTime) ; double dReadTime, dWriteTime ; stCopySize = stTimes ; std::vector<size_t> inVect ; std::vector<size_t> outVect ; std::set<size_t> outSet ; std::set<size_t> inSet ; // Prepare vector and set do { stPos = (size_t)(::rand()<<16) % stSize ; outVect.push_back(stPos) ; outSet.insert(stPos) ; stPos = (size_t)(::rand()<<16) % stSize ; inVect.push_back(stPos) ; inSet.insert(stPos) ; } while (--stCopySize) ; // Write & read using vectors if ( !bReverse && !bOrdered ) { std::vector<size_t>::iterator outI, inI ; outI = outVect.begin() ; inI = inVect.begin() ; stCopySize = stTimes ; dReadTime = 0.0 ; dWriteTime = 0.0 ; do { dTime = RealTime_Microsecs() ; fFile.seekp(*outI) ; fFile.write(pPattern, stBytes) ; dWriteTime += RealTime_Microsecs() - dTime ; ++outI ; if ( !bWriteOnly ) { dTime = RealTime_Microsecs() ; fFile.seekg(*inI) ; fFile.read(pReadBuf, stBytes) ; dReadTime += RealTime_Microsecs() - dTime ; ++inI ; } } while (--stCopySize) ; std::cout << "Write time is " << xw::str::itoa(dWriteTime, 5, 'f') << " (Ave: " << xw::str::itoa(dWriteTime/stTimes, 10, 'f') << ")" << std::endl ; if ( !bWriteOnly ) { std::cout << "Read time is " << xw::str::itoa(dReadTime, 5, 'f') << " (Ave: " << xw::str::itoa(dReadTime/stTimes, 10, 'f') << ")" << std::endl ; } } // End // Write in order if ( bOrdered ) { std::set<size_t>::iterator i = outSet.begin() ; dWriteTime = 0.0 ; stCopySize = 0 ; for(; i != outSet.end(); ++i) { stPos = *i ; dTime = RealTime_Microsecs() ; fFile.seekp(stPos) ; fFile.write(pPattern, stBytes) ; dWriteTime += RealTime_Microsecs() - dTime ; ++stCopySize ; } std::cout << "Ordered Write time is " << xw::str::itoa(dWriteTime, 5, 'f') << " in " << xw::str::itoa(stCopySize) << " (Ave: " << xw::str::itoa(dWriteTime/stCopySize, 10, 'f') << ")" << std::endl ; if ( !bWriteOnly ) { i = inSet.begin() ; dReadTime = 0.0 ; stCopySize = 0 ; for(; i != inSet.end(); ++i) { stPos = *i ; dTime = RealTime_Microsecs() ; fFile.seekg(stPos) ; fFile.read(pReadBuf, stBytes) ; dReadTime += RealTime_Microsecs() - dTime ; ++stCopySize ; } std::cout << "Ordered Read time is " << xw::str::itoa(dReadTime, 5, 'f') << " in " << xw::str::itoa(stCopySize) << " (Ave: " << xw::str::itoa(dReadTime/stCopySize, 10, 'f') << ")" << std::endl ; } }// End // Write in reverse order if ( bReverse ) { std::set<size_t>::reverse_iterator i = outSet.rbegin() ; dWriteTime = 0.0 ; stCopySize = 0 ; for(; i != outSet.rend(); ++i) { stPos = *i ; dTime = RealTime_Microsecs() ; fFile.seekp(stPos) ; fFile.write(pPattern, stBytes) ; dWriteTime += RealTime_Microsecs() - dTime ; ++stCopySize ; } std::cout << "Reverse ordered Write time is " << xw::str::itoa(dWriteTime, 5, 'f') << " in " << xw::str::itoa(stCopySize) << " (Ave: " << xw::str::itoa(dWriteTime/stCopySize, 10, 'f') << ")" << std::endl ; if ( !bWriteOnly ) { i = inSet.rbegin() ; dReadTime = 0.0 ; stCopySize = 0 ; for(; i != inSet.rend(); ++i) { stPos = *i ; dTime = RealTime_Microsecs() ; fFile.seekg(stPos) ; fFile.read(pReadBuf, stBytes) ; dReadTime += RealTime_Microsecs() - dTime ; ++stCopySize ; } std::cout << "Reverse ordered Read time is " << xw::str::itoa(dReadTime, 5, 'f') << " in " << xw::str::itoa(stCopySize) << " (Ave: " << xw::str::itoa(dReadTime/stCopySize, 10, 'f') << ")" << std::endl ; } }// End dTime = RealTime_Microsecs() ; fFile.close() ; std::cout << "Flush/Close Time is " << xw::str::itoa(RealTime_Microsecs()-dTime, 5, 'f') << std::endl ; std::cout << "Program Terminated" << std::endl ; } catch(...) { std::cout << "Something wrong or wrong parameters" << std::endl ; retval = -1 ; } if ( p ) delete []p ; if ( pPattern ) delete []pPattern ; if ( pReadBuf ) delete []pReadBuf ; return retval ; }

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• c++ optimize array of ints

  - by a432511

  I have a 2D lookup table of int16_t. int16_t my_array[37][73] = {{**DATA HERE**}} I have a mixture of values that range from just above the range of int8_t to just below the range of int8_t and some of the values repeat themselves. I am trying to reduce the size of this lookup table. What I have done so far is split each int16_t value into two int8_t values to visualize the wasted bytes. int8_t part_1 = original_value >> 4; int8_t part_2 = original_value & 0x0000FFFF; // If the upper 4 bits of the original_value were empty if(part_1 == 0) wasted_bytes_count++; I can easily remove the zero value int8_t that are wasting a byte of space and I can also remove the duplicate values, but my question is how do I do remove those values while retaining the ability to lookup based on the two indices? I contemplated translating this into a 1D array and adding a number following each duplicated value that would represent the number of duplicates that were removed, but I am struggling with how I would then identify what is a lookup value and what is a duplicate count. Also, it is further complicated by stripping out the zero int8_t values that were wasted bytes. EDIT: This array is stored in ROM already. RAM is even more limited than ROM so it is already stored in ROM. EDIT: I am going to post a bounty for this question as soon as I can. I need a complete answer of how to store the information AND retrieve it. It does not need to be a 2D array as long as I can get the same values. EDIT: Adding the actual array below: {150,145,140,135,130,125,120,115,110,105,100,95,90,85,80,75,70,65,60,55,50,45,40,35,30,25,20,15,10,5,0,-4,-9,-14,-19,-24,-29,-34,-39,-44,-49,-54,-59,-64,-69,-74,-79,-84,-89,-94,-99,104,109,114,119,124,129,134,139,144,149,154,159,164,169,174,179,175,170,165,160,155,150}, \ {143,137,131,126,120,115,110,105,100,95,90,85,80,75,71,66,62,57,53,48,44,39,35,31,27,22,18,14,9,5,1,-3,-7,-11,-16,-20,-25,-29,-34,-38,-43,-47,-52,-57,-61,-66,-71,-76,-81,-86,-91,-96,101,107,112,117,123,128,134,140,146,151,157,163,169,175,178,172,166,160,154,148,143}, \ {130,124,118,112,107,101,96,92,87,82,78,74,70,65,61,57,54,50,46,42,38,34,31,27,23,19,16,12,8,4,1,-2,-6,-10,-14,-18,-22,-26,-30,-34,-38,-43,-47,-51,-56,-61,-65,-70,-75,-79,-84,-89,-94,100,105,111,116,122,128,135,141,148,155,162,170,177,174,166,159,151,144,137,130}, \ {111,104,99,94,89,85,81,77,73,70,66,63,60,56,53,50,46,43,40,36,33,30,26,23,20,16,13,10,6,3,0,-3,-6,-9,-13,-16,-20,-24,-28,-32,-36,-40,-44,-48,-52,-57,-61,-65,-70,-74,-79,-84,-88,-93,-98,103,109,115,121,128,135,143,152,162,172,176,165,154,144,134,125,118,111}, \ {85,81,77,74,71,68,65,63,60,58,56,53,51,49,46,43,41,38,35,32,29,26,23,19,16,13,10,7,4,1,-1,-3,-6,-9,-13,-16,-19,-23,-26,-30,-34,-38,-42,-46,-50,-54,-58,-62,-66,-70,-74,-78,-83,-87,-91,-95,100,105,110,117,124,133,144,159,178,160,141,125,112,103,96,90,85}, \ {62,60,58,57,55,54,52,51,50,48,47,46,44,42,41,39,36,34,31,28,25,22,19,16,13,10,7,4,2,0,-3,-5,-8,-10,-13,-16,-19,-22,-26,-29,-33,-37,-41,-45,-49,-53,-56,-60,-64,-67,-70,-74,-77,-80,-83,-86,-89,-91,-94,-97,101,105,111,130,109,84,77,74,71,68,66,64,62}, \ {46,46,45,44,44,43,42,42,41,41,40,39,38,37,36,35,33,31,28,26,23,20,16,13,10,7,4,1,-1,-3,-5,-7,-9,-12,-14,-16,-19,-22,-26,-29,-33,-36,-40,-44,-48,-51,-55,-58,-61,-64,-66,-68,-71,-72,-74,-74,-75,-74,-72,-68,-61,-48,-25,2,22,33,40,43,45,46,47,46,46}, \ {36,36,36,36,36,35,35,35,35,34,34,34,34,33,32,31,30,28,26,23,20,17,14,10,6,3,0,-2,-4,-7,-9,-10,-12,-14,-15,-17,-20,-23,-26,-29,-32,-36,-40,-43,-47,-50,-53,-56,-58,-60,-62,-63,-64,-64,-63,-62,-59,-55,-49,-41,-30,-17,-4,6,15,22,27,31,33,34,35,36,36}, \ {30,30,30,30,30,30,30,29,29,29,29,29,29,29,29,28,27,26,24,21,18,15,11,7,3,0,-3,-6,-9,-11,-12,-14,-15,-16,-17,-19,-21,-23,-26,-29,-32,-35,-39,-42,-45,-48,-51,-53,-55,-56,-57,-57,-56,-55,-53,-49,-44,-38,-31,-23,-14,-6,0,7,13,17,21,24,26,27,29,29,30}, \ {25,25,26,26,26,25,25,25,25,25,25,25,25,26,25,25,24,23,21,19,16,12,8,4,0,-3,-7,-10,-13,-15,-16,-17,-18,-19,-20,-21,-22,-23,-25,-28,-31,-34,-37,-40,-43,-46,-48,-49,-50,-51,-51,-50,-48,-45,-42,-37,-32,-26,-19,-13,-7,-1,3,7,11,14,17,19,21,23,24,25,25}, \ {21,22,22,22,22,22,22,22,22,22,22,22,22,22,22,22,21,20,18,16,13,9,5,1,-3,-7,-11,-14,-17,-18,-20,-21,-21,-22,-22,-22,-23,-23,-25,-27,-29,-32,-35,-37,-40,-42,-44,-45,-45,-45,-44,-42,-40,-36,-32,-27,-22,-17,-12,-7,-3,0,3,7,9,12,14,16,18,19,20,21,21}, \ {18,19,19,19,19,19,19,19,19,19,19,19,19,19,19,19,18,17,16,14,10,7,2,-1,-6,-10,-14,-17,-19,-21,-22,-23,-24,-24,-24,-24,-23,-23,-23,-24,-26,-28,-30,-33,-35,-37,-38,-39,-39,-38,-36,-34,-31,-28,-24,-19,-15,-10,-6,-3,0,1,4,6,8,10,12,14,15,16,17,18,18}, \ {16,16,17,17,17,17,17,17,17,17,17,16,16,16,16,16,16,15,13,11,8,4,0,-4,-9,-13,-16,-19,-21,-23,-24,-25,-25,-25,-25,-24,-23,-21,-20,-20,-21,-22,-24,-26,-28,-30,-31,-32,-31,-30,-29,-27,-24,-21,-17,-13,-9,-6,-3,-1,0,2,4,5,7,9,10,12,13,14,15,16,16}, \ {14,14,14,15,15,15,15,15,15,15,14,14,14,14,14,14,13,12,11,9,5,2,-2,-6,-11,-15,-18,-21,-23,-24,-25,-25,-25,-25,-24,-22,-21,-18,-16,-15,-15,-15,-17,-19,-21,-22,-24,-24,-24,-23,-22,-20,-18,-15,-12,-9,-5,-3,-1,0,1,2,4,5,6,8,9,10,11,12,13,14,14}, \ {12,13,13,13,13,13,13,13,13,13,13,13,12,12,12,12,11,10,9,6,3,0,-4,-8,-12,-16,-19,-21,-23,-24,-24,-24,-24,-23,-22,-20,-17,-15,-12,-10,-9,-9,-10,-12,-13,-15,-17,-17,-18,-17,-16,-15,-13,-11,-8,-5,-3,-1,0,1,1,2,3,4,6,7,8,9,10,11,12,12,12}, \ {11,11,11,11,11,12,12,12,12,12,11,11,11,11,11,10,10,9,7,5,2,-1,-5,-9,-13,-17,-20,-22,-23,-23,-23,-23,-22,-20,-18,-16,-14,-11,-9,-6,-5,-4,-5,-6,-8,-9,-11,-12,-12,-12,-12,-11,-9,-8,-6,-3,-1,0,0,1,1,2,3,4,5,6,7,8,9,10,11,11,11}, \ {10,10,10,10,10,10,10,10,10,10,10,10,10,10,9,9,9,7,6,3,0,-3,-6,-10,-14,-17,-20,-21,-22,-22,-22,-21,-19,-17,-15,-13,-10,-8,-6,-4,-2,-2,-2,-2,-4,-5,-7,-8,-8,-9,-8,-8,-7,-5,-4,-2,0,0,1,1,1,2,2,3,4,5,6,7,8,9,10,10,10}, \ {9,9,9,9,9,9,9,10,10,9,9,9,9,9,9,8,8,6,5,2,0,-4,-7,-11,-15,-17,-19,-21,-21,-21,-20,-18,-16,-14,-12,-10,-8,-6,-4,-2,-1,0,0,0,-1,-2,-4,-5,-5,-6,-6,-5,-5,-4,-3,-1,0,0,1,1,1,1,2,3,3,5,6,7,8,8,9,9,9}, \ {9,9,9,9,9,9,9,9,9,9,9,9,8,8,8,8,7,5,4,1,-1,-5,-8,-12,-15,-17,-19,-20,-20,-19,-18,-16,-14,-11,-9,-7,-5,-4,-2,-1,0,0,1,1,0,0,-2,-3,-3,-4,-4,-4,-3,-3,-2,-1,0,0,0,0,0,1,1,2,3,4,5,6,7,8,8,9,9}, \ {9,9,9,8,8,8,9,9,9,9,9,8,8,8,8,7,6,5,3,0,-2,-5,-9,-12,-15,-17,-18,-19,-19,-18,-16,-14,-12,-9,-7,-5,-4,-2,-1,0,0,1,1,1,1,0,0,-1,-2,-2,-3,-3,-2,-2,-1,-1,0,0,0,0,0,0,0,1,2,3,4,5,6,7,8,8,9}, \ {8,8,8,8,8,8,9,9,9,9,9,9,8,8,8,7,6,4,2,0,-3,-6,-9,-12,-15,-17,-18,-18,-17,-16,-14,-12,-10,-8,-6,-4,-2,-1,0,0,1,2,2,2,2,1,0,0,-1,-1,-1,-2,-2,-1,-1,0,0,0,0,0,0,0,0,0,1,2,3,4,5,6,7,8,8}, \ {8,8,8,8,9,9,9,9,9,9,9,9,9,8,8,7,5,3,1,-1,-4,-7,-10,-13,-15,-16,-17,-17,-16,-15,-13,-11,-9,-6,-5,-3,-2,0,0,0,1,2,2,2,2,1,1,0,0,0,-1,-1,-1,-1,-1,0,0,0,0,-1,-1,-1,-1,-1,0,0,1,3,4,5,7,7,8}, \ {8,8,9,9,9,9,10,10,10,10,10,10,10,9,8,7,5,3,0,-2,-5,-8,-11,-13,-15,-16,-16,-16,-15,-13,-12,-10,-8,-6,-4,-2,-1,0,0,1,2,2,3,3,2,2,1,0,0,0,0,0,0,0,0,0,0,-1,-1,-2,-2,-2,-2,-2,-1,0,0,1,3,4,6,7,8}, \ {7,8,9,9,9,10,10,11,11,11,11,11,10,10,9,7,5,3,0,-2,-6,-9,-11,-13,-15,-16,-16,-15,-14,-13,-11,-9,-7,-5,-3,-2,0,0,1,1,2,3,3,3,3,2,2,1,1,0,0,0,0,0,0,0,-1,-1,-2,-3,-3,-4,-4,-4,-3,-2,-1,0,1,3,5,6,7}, \ {6,8,9,9,10,11,11,12,12,12,12,12,11,11,9,7,5,2,0,-3,-7,-10,-12,-14,-15,-16,-15,-15,-13,-12,-10,-8,-7,-5,-3,-1,0,0,1,2,2,3,3,4,3,3,3,2,2,1,1,1,0,0,0,0,-1,-2,-3,-4,-4,-5,-5,-5,-5,-4,-2,-1,0,2,3,5,6}, \ {6,7,8,10,11,12,12,13,13,14,14,13,13,11,10,8,5,2,0,-4,-8,-11,-13,-15,-16,-16,-16,-15,-13,-12,-10,-8,-6,-5,-3,-1,0,0,1,2,3,3,4,4,4,4,4,3,3,3,2,2,1,1,0,0,-1,-2,-3,-5,-6,-7,-7,-7,-6,-5,-4,-3,-1,0,2,4,6}, \ {5,7,8,10,11,12,13,14,15,15,15,14,14,12,11,8,5,2,-1,-5,-9,-12,-14,-16,-17,-17,-16,-15,-14,-12,-11,-9,-7,-5,-3,-1,0,0,1,2,3,4,4,5,5,5,5,5,5,4,4,3,3,2,1,0,-1,-2,-4,-6,-7,-8,-8,-8,-8,-7,-6,-4,-2,0,1,3,5}, \ {4,6,8,10,12,13,14,15,16,16,16,16,15,13,11,9,5,2,-2,-6,-10,-13,-16,-17,-18,-18,-17,-16,-15,-13,-11,-9,-7,-5,-4,-2,0,0,1,3,3,4,5,6,6,7,7,7,7,7,6,5,4,3,2,0,-1,-3,-5,-7,-8,-9,-10,-10,-10,-9,-7,-5,-4,-1,0,2,4}, \ {4,6,8,10,12,14,15,16,17,18,18,17,16,15,12,9,5,1,-3,-8,-12,-15,-18,-19,-20,-20,-19,-18,-16,-15,-13,-11,-8,-6,-4,-2,-1,0,1,3,4,5,6,7,8,9,9,9,9,9,9,8,7,5,3,1,-1,-3,-6,-8,-10,-11,-12,-12,-11,-10,-9,-7,-5,-2,0,1,4}, \ {4,6,8,11,13,15,16,18,19,19,19,19,18,16,13,10,5,0,-5,-10,-15,-18,-21,-22,-23,-22,-22,-20,-18,-17,-14,-12,-10,-8,-5,-3,-1,0,1,3,5,6,8,9,10,11,12,12,13,12,12,11,9,7,5,2,0,-3,-6,-9,-11,-12,-13,-13,-12,-11,-10,-8,-6,-3,-1,1,4}, \ {3,6,9,11,14,16,17,19,20,21,21,21,19,17,14,10,4,-1,-8,-14,-19,-22,-25,-26,-26,-26,-25,-23,-21,-19,-17,-14,-12,-9,-7,-4,-2,0,1,3,5,7,9,11,13,14,15,16,16,16,16,15,13,10,7,4,0,-3,-7,-10,-12,-14,-15,-14,-14,-12,-11,-9,-6,-4,-1,1,3}, \ {4,6,9,12,14,17,19,21,22,23,23,23,21,19,15,9,2,-5,-13,-20,-25,-28,-30,-31,-31,-30,-29,-27,-25,-22,-20,-17,-14,-11,-9,-6,-3,0,1,4,6,9,11,13,15,17,19,20,21,21,21,20,18,15,11,6,2,-2,-7,-11,-13,-15,-16,-16,-15,-13,-11,-9,-7,-4,-1,1,4}, \ {4,7,10,13,15,18,20,22,24,25,25,25,23,20,15,7,-2,-12,-22,-29,-34,-37,-38,-38,-37,-36,-34,-31,-29,-26,-23,-20,-17,-13,-10,-7,-4,-1,2,5,8,11,13,16,18,21,23,24,26,26,26,26,24,21,17,12,5,0,-6,-10,-14,-16,-16,-16,-15,-14,-12,-10,-7,-4,-1,1,4}, \ {4,7,10,13,16,19,22,24,26,27,27,26,24,19,11,-1,-15,-28,-37,-43,-46,-47,-47,-45,-44,-41,-39,-36,-32,-29,-26,-22,-19,-15,-11,-8,-4,-1,2,5,9,12,15,19,22,24,27,29,31,33,33,33,32,30,26,21,14,6,0,-6,-11,-14,-15,-16,-15,-14,-12,-9,-7,-4,-1,1,4}, \ {6,9,12,15,18,21,23,25,27,28,27,24,17,4,-14,-34,-49,-56,-60,-60,-60,-58,-56,-53,-50,-47,-43,-40,-36,-32,-28,-25,-21,-17,-13,-9,-5,-1,2,6,10,14,17,21,24,28,31,34,37,39,41,42,43,43,41,38,33,25,17,8,0,-4,-8,-10,-10,-10,-8,-7,-4,-2,0,3,6}, \ {22,24,26,28,30,32,33,31,23,-18,-81,-96,-99,-98,-95,-93,-89,-86,-82,-78,-74,-70,-66,-62,-57,-53,-49,-44,-40,-36,-32,-27,-23,-19,-14,-10,-6,-1,2,6,10,15,19,23,27,31,35,38,42,45,49,52,55,57,60,61,63,63,62,61,57,53,47,40,33,28,23,21,19,19,19,20,22}, \ {168,173,178,176,171,166,161,156,151,146,141,136,131,126,121,116,111,106,101,-96,-91,-86,-81,-76,-71,-66,-61,-56,-51,-46,-41,-36,-31,-26,-21,-16,-11,-6,-1,3,8,13,18,23,28,33,38,43,48,53,58,63,68,73,78,83,88,93,98,103,108,113,118,123,128,133,138,143,148,153,158,163,168}, \ Thanks for your time.

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• Very different IO performance in C/C++

  - by Roberto Tirabassi

  Hi all, I'm a new user and my english is not so good so I hope to be clear. We're facing a performance problem using large files (1GB or more) expecially (as it seems) when you try to grow them in size. Anyway... to verify our sensations we tryed the following (on Win 7 64Bit, 4core, 8GB Ram, 32 bit code compiled with VC2008) a) Open an unexisting file. Write it from the beginning up to 1Gb in 1Mb slots. Now you have a 1Gb file. Now randomize 10000 positions within that file, seek to that position and write 50 bytes in each position, no matter what you write. Close the file and look at the results. Time to create the file is quite fast (about 0.3"), time to write 10000 times is fast all the same (about 0.03"). Very good, this is the beginnig. Now try something else... b) Open an unexisting file, seek to 1Gb-1byte and write just 1 byte. Now you have another 1Gb file. Follow the next steps exactly same way of case 'a', close the file and look at the results. Time to create the file is the faster you can imagine (about 0.00009") but write time is something you can't believe.... about 90"!!!!! b.1) Open an unexisting file, don't write any byte. Act as before, ramdomizing, seeking and writing, close the file and look at the result. Time to write is long all the same: about 90"!!!!! Ok... this is quite amazing. But there's more! c) Open again the file you crated in case 'a', don't truncate it... randomize again 10000 positions and act as before. You're fast as before, about 0,03" to write 10000 times. This sounds Ok... try another step. d) Now open the file you created in case 'b', don't truncate it... randomize again 10000 positions and act as before. You're slow again and again, but the time is reduced to... 45"!! Maybe, trying again, the time will reduce. I actually wonder why... Any Idea? The following is part of the code I used to test what I told in previuos cases (you'll have to change someting in order to have a clean compilation, I just cut & paste from some source code, sorry). The sample can read and write, in random, ordered or reverse ordered mode, but write only in random order is the clearest test. We tryed using std::fstream but also using directly CreateFile(), WriteFile() and so on the results are the same (even if std::fstream is actually a little slower). Parameters for case 'a' = -f_tempdir_\casea.dat -n10000 -t -p -w Parameters for case 'b' = -f_tempdir_\caseb.dat -n10000 -t -v -w Parameters for case 'b.1' = -f_tempdir_\caseb.dat -n10000 -t -w Parameters for case 'c' = -f_tempdir_\casea.dat -n10000 -w Parameters for case 'd' = -f_tempdir_\caseb.dat -n10000 -w Run the test (and even others) and see... // iotest.cpp : Defines the entry point for the console application. // #include <windows.h> #include <iostream> #include <set> #include <vector> #include "stdafx.h" double RealTime_Microsecs() { LARGE_INTEGER fr = {0, 0}; LARGE_INTEGER ti = {0, 0}; double time = 0.0; QueryPerformanceCounter(&ti); QueryPerformanceFrequency(&fr); time = (double) ti.QuadPart / (double) fr.QuadPart; return time; } int main(int argc, char* argv[]) { std::string sFileName ; size_t stSize, stTimes, stBytes ; int retval = 0 ; char *p = NULL ; char *pPattern = NULL ; char *pReadBuf = NULL ; try { // Default stSize = 1<<30 ; // 1Gb stTimes = 1000 ; stBytes = 50 ; bool bTruncate = false ; bool bPre = false ; bool bPreFast = false ; bool bOrdered = false ; bool bReverse = false ; bool bWriteOnly = false ; // Comsumo i parametri for(int index=1; index < argc; ++index) { if ( '-' != argv[index][0] ) throw ; switch(argv[index][1]) { case 'f': sFileName = argv[index]+2 ; break ; case 's': stSize = xw::str::strtol(argv[index]+2) ; break ; case 'n': stTimes = xw::str::strtol(argv[index]+2) ; break ; case 'b':stBytes = xw::str::strtol(argv[index]+2) ; break ; case 't': bTruncate = true ; break ; case 'p' : bPre = true, bPreFast = false ; break ; case 'v' : bPreFast = true, bPre = false ; break ; case 'o' : bOrdered = true, bReverse = false ; break ; case 'r' : bReverse = true, bOrdered = false ; break ; case 'w' : bWriteOnly = true ; break ; default: throw ; break ; } } if ( sFileName.empty() ) { std::cout << "Usage: -f<File Name> -s<File Size> -n<Number of Reads and Writes> -b<Bytes per Read and Write> -t -p -v -o -r -w" << std::endl ; std::cout << "-t truncates the file, -p pre load the file, -v pre load 'veloce', -o writes in order mode, -r write in reverse order mode, -w Write Only" << std::endl ; std::cout << "Default: 1Gb, 1000 times, 50 bytes" << std::endl ; throw ; } if ( !stSize || !stTimes || !stBytes ) { std::cout << "Invalid Parameters" << std::endl ; return -1 ; } size_t stBestSize = 0x00100000 ; std::fstream fFile ; fFile.open(sFileName.c_str(), std::ios_base::binary|std::ios_base::out|std::ios_base::in|(bTruncate?std::ios_base::trunc:0)) ; p = new char[stBestSize] ; pPattern = new char[stBytes] ; pReadBuf = new char[stBytes] ; memset(p, 0, stBestSize) ; memset(pPattern, (int)(stBytes&0x000000ff), stBytes) ; double dTime = RealTime_Microsecs() ; size_t stCopySize, stSizeToCopy = stSize ; if ( bPre ) { do { stCopySize = std::min(stSizeToCopy, stBestSize) ; fFile.write(p, stCopySize) ; stSizeToCopy -= stCopySize ; } while (stSizeToCopy) ; std::cout << "Creating time is: " << xw::str::itoa(RealTime_Microsecs()-dTime, 5, 'f') << std::endl ; } else if ( bPreFast ) { fFile.seekp(stSize-1) ; fFile.write(p, 1) ; std::cout << "Creating Fast time is: " << xw::str::itoa(RealTime_Microsecs()-dTime, 5, 'f') << std::endl ; } size_t stPos ; ::srand((unsigned int)dTime) ; double dReadTime, dWriteTime ; stCopySize = stTimes ; std::vector<size_t> inVect ; std::vector<size_t> outVect ; std::set<size_t> outSet ; std::set<size_t> inSet ; // Prepare vector and set do { stPos = (size_t)(::rand()<<16) % stSize ; outVect.push_back(stPos) ; outSet.insert(stPos) ; stPos = (size_t)(::rand()<<16) % stSize ; inVect.push_back(stPos) ; inSet.insert(stPos) ; } while (--stCopySize) ; // Write & read using vectors if ( !bReverse && !bOrdered ) { std::vector<size_t>::iterator outI, inI ; outI = outVect.begin() ; inI = inVect.begin() ; stCopySize = stTimes ; dReadTime = 0.0 ; dWriteTime = 0.0 ; do { dTime = RealTime_Microsecs() ; fFile.seekp(*outI) ; fFile.write(pPattern, stBytes) ; dWriteTime += RealTime_Microsecs() - dTime ; ++outI ; if ( !bWriteOnly ) { dTime = RealTime_Microsecs() ; fFile.seekg(*inI) ; fFile.read(pReadBuf, stBytes) ; dReadTime += RealTime_Microsecs() - dTime ; ++inI ; } } while (--stCopySize) ; std::cout << "Write time is " << xw::str::itoa(dWriteTime, 5, 'f') << " (Ave: " << xw::str::itoa(dWriteTime/stTimes, 10, 'f') << ")" << std::endl ; if ( !bWriteOnly ) { std::cout << "Read time is " << xw::str::itoa(dReadTime, 5, 'f') << " (Ave: " << xw::str::itoa(dReadTime/stTimes, 10, 'f') << ")" << std::endl ; } } // End // Write in order if ( bOrdered ) { std::set<size_t>::iterator i = outSet.begin() ; dWriteTime = 0.0 ; stCopySize = 0 ; for(; i != outSet.end(); ++i) { stPos = *i ; dTime = RealTime_Microsecs() ; fFile.seekp(stPos) ; fFile.write(pPattern, stBytes) ; dWriteTime += RealTime_Microsecs() - dTime ; ++stCopySize ; } std::cout << "Ordered Write time is " << xw::str::itoa(dWriteTime, 5, 'f') << " in " << xw::str::itoa(stCopySize) << " (Ave: " << xw::str::itoa(dWriteTime/stCopySize, 10, 'f') << ")" << std::endl ; if ( !bWriteOnly ) { i = inSet.begin() ; dReadTime = 0.0 ; stCopySize = 0 ; for(; i != inSet.end(); ++i) { stPos = *i ; dTime = RealTime_Microsecs() ; fFile.seekg(stPos) ; fFile.read(pReadBuf, stBytes) ; dReadTime += RealTime_Microsecs() - dTime ; ++stCopySize ; } std::cout << "Ordered Read time is " << xw::str::itoa(dReadTime, 5, 'f') << " in " << xw::str::itoa(stCopySize) << " (Ave: " << xw::str::itoa(dReadTime/stCopySize, 10, 'f') << ")" << std::endl ; } }// End // Write in reverse order if ( bReverse ) { std::set<size_t>::reverse_iterator i = outSet.rbegin() ; dWriteTime = 0.0 ; stCopySize = 0 ; for(; i != outSet.rend(); ++i) { stPos = *i ; dTime = RealTime_Microsecs() ; fFile.seekp(stPos) ; fFile.write(pPattern, stBytes) ; dWriteTime += RealTime_Microsecs() - dTime ; ++stCopySize ; } std::cout << "Reverse ordered Write time is " << xw::str::itoa(dWriteTime, 5, 'f') << " in " << xw::str::itoa(stCopySize) << " (Ave: " << xw::str::itoa(dWriteTime/stCopySize, 10, 'f') << ")" << std::endl ; if ( !bWriteOnly ) { i = inSet.rbegin() ; dReadTime = 0.0 ; stCopySize = 0 ; for(; i != inSet.rend(); ++i) { stPos = *i ; dTime = RealTime_Microsecs() ; fFile.seekg(stPos) ; fFile.read(pReadBuf, stBytes) ; dReadTime += RealTime_Microsecs() - dTime ; ++stCopySize ; } std::cout << "Reverse ordered Read time is " << xw::str::itoa(dReadTime, 5, 'f') << " in " << xw::str::itoa(stCopySize) << " (Ave: " << xw::str::itoa(dReadTime/stCopySize, 10, 'f') << ")" << std::endl ; } }// End dTime = RealTime_Microsecs() ; fFile.close() ; std::cout << "Flush/Close Time is " << xw::str::itoa(RealTime_Microsecs()-dTime, 5, 'f') << std::endl ; std::cout << "Program Terminated" << std::endl ; } catch(...) { std::cout << "Something wrong or wrong parameters" << std::endl ; retval = -1 ; } if ( p ) delete []p ; if ( pPattern ) delete []pPattern ; if ( pReadBuf ) delete []pReadBuf ; return retval ; }

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