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  • Performance of std::pow - cache misses???

    - by Eamon Nerbonne
    I've been trying to optimize a numeric program of mine, and have run into something of a mystery. I'm looping over code that performs thousands of floating point operations, and just 1 call to pow nevertheless, that call takes 5% of the time... That's not necessarily a critical issue, but it is odd, so I'd like to understand what's happening. When I profiled for cache misses, VS.NET 2010RC's profiler reports that virtually all cache misses are occurring in std::pow... so... what's up with that? Is there a faster alternative? I tried powf, but that's only slightly faster; it's still responsible for an abnormal number of cache misses. Why would a basic function like pow cause cache-misses?

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  • Looking for a good book on microprocessor internals

    - by David Holm
    I'm looking for a good book on how modern microprocessors are designed and work as I would like to increase my understanding of what makes them tick. Something that covers pipelines, superscalar architectures, caches etc. A book that is suitable for a programmer with several years of experience and has done and understands assembly programming and machine language, so basically not "CPUs for Dummies" or anything such. What books do people who design today's processors read for instance?

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  • branch prediction

    - by Alexander
    Consider the following sequence of actual outcomes for a single static branch. T means the branch is taken. N means the branch is not taken. For this question, assume that this is the only branch in the program. T T T N T N T T T N T N T T T N T N Assume a two-level branch predictor that uses one bit of branch history—i.e., a one-bit BHR. Since there is only one branch in the program, it does not matter how the BHR is concatenated with the branch PC to index the BHT. Assume that the BHT uses one-bit counters and that, again, all entries are initialized to N. Which of the branches in this sequence would be mis-predicted? Use the table below. Now I am not asking answers to this question, rather than guides and pointers on this. What does a two level branch predictor means and how does it works? What does the BHR and BHT stands for?

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  • cache memory performance

    - by Krewie
    Hello, i just have a general question about cache memory. How would a program perform badly on a cache based system ? , since cache memory stores adresses from main memory that is requested, aswell as adresses that ranges around the same adress as the one copied from the main memory.

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  • Why is the JVM stack-based and the DalvikVM register based?

    - by aioobe
    I'm curious, why did Sun decide to make the JVM stack-based and Google decide to make the DalvikVM register based? I suppose the JVM can't really assume that a certain number of registers are available on the target platform, since it is supposed to be platform independent. Therefor it just postpones the register-allocation etc, to the JIT compiler. (Correct me if I'm wrong.) So the Android guys thought, "hey, that's inefficient, let's go for a register based vm right away..."? But wait, there are multiple different android devices, what number of registers did the Dalvik target? Are the Dalvik opcodes hardcoded for a certain number of registers? Do all current Android devices on the market have about the same number of registers? Or, is there a register re-allocation performed during dex-loading? How does all this fit together?

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  • Best CPUs for speeding up compiling times of C++ w/ DistGCC

    - by Jay
    I'm putting together a distributed build farm with DistGCC to speed up our teams compile times and just looking for thoughts on which processors to use in the hosts. Are we going to get a noticeable decrease in time using 8 cores vs. 4-hyperthreaded cores? Big difference in time between i7 and Xeon? etc, etc. Just need advice from people who've put together kick-a build clusters. We've got a majority of the normal things to speed up builds in place (pre-compiled headers, ccache, local gigabit connections between them, tons of ram, etc) so please just give advice on the best processor to use. And money is a factor, but anythings doable if the performance increase is noticeable. Thanks. Jay

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  • Could this code damage my processor??!!

    - by Osama Gamal
    A friend sent me that code and alleges that it could damage the processor. Is that true? void damage_processor() { while (true) { // Assembly code that sets the five control registers bits to ones which causes a bunch of exceptions in the system and then damages the processor Asm( "mov cr0, 0xffffffff \n\t" "mov cr1, 0xffffffff \n\t" "mov cr2, 0xffffffff \n\t" "mov cr3, 0xffffffff \n\t" "mov cr4, 0xffffffff \n\t" ) } } Is that true?

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  • P6 Architecture - Register renaming aside, does the limited user registers result in more ops spent

    - by mrjoltcola
    I'm studying JIT design with regard to dynamic languages VM implementation. I haven't done much Assembly since the 8086/8088 days, just a little here or there, so be nice if I'm out of sorts. As I understand it, the x86 (IA-32) architecture still has the same basic limited register set today that it always did, but the internal register count has grown tremendously, but these internal registers are not generally available and are used with register renaming to achieve parallel pipelining of code that otherwise could not be parallelizable. I understand this optimization pretty well, but my feeling is, while these optimizations help in overall throughput and for parallel algorithms, the limited register set we are still stuck with results in more register spilling overhead such that if x86 had double, or quadruple the registers available to us, there may be significantly less push/pop opcodes in a typical instruction stream? Or are there other processor optmizations that also optimize this away that I am unaware of? Basically if I've a unit of code that has 4 registers to work with for integer work, but my unit has a dozen variables, I've got potentially a push/pop for every 2 or so instructions. Any references to studies, or better yet, personal experiences?

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  • how to optimize illustrator artwork in flash?

    - by sasi
    I'm working on a flash project that incorporates a lot of artwork done in Illustrator CS4. I've been copy-pasting directly from Illustrator into Flash, and I add some animations as well. Final file is going to be a one single swf file which will be a part of UI for an application and .net will be the core for this. But now flash becomes unusable slow to respond for actions. My machine is a fast i7 with 6gb of RAM, so I don't think that's the issue. We are going to use this file with dual core atom processors. Does anyone have ideas for alternative importing techniques, optimizations within illustrator, anything at all that will make this more manageable? Thanks

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  • How to know when the kernel was last compiled? [closed]

    - by Mehmet Tuncal
    I have installed a linux distro and I "think" it is vulnerable to kernel exploits. I have to update kernel but I need to know if it is really compiled in year 2003? How can I know if additional updates are made to the kernel? Linux gandalf 2.4.21-4.ELsmp #1 SMP Fri Oct 3 17:52:56 EDT 2003 i686 i686 i386 GNU/Linux Does also "smp" mean that it is safe from latest threats or something? Thank you.

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  • Working with ieee format numbers in ARM

    - by Jake Sellers
    I'm trying to write an ARM program that will convert an ieee number to a TNS format number. TNS is a format used by some super computers, and is similar to ieee but different. I'm trying to use several masks to place the three different "part" of the ieee number in separate registers so I can move them around accordingly. Here is my unpack subroutine: UnpackIEEE LDR r1, SMASK ;load the sign bit mask into r1 LDR r2, EMASK ;load the exponent mask into r2 LDR r3, GMASK ;load the significand mask into r3 AND r4, r0, r1 ;apply sign mask to IEEE and save into r4 AND r5, r0, r2 ;apply exponent mask to IEEE and save into r5 AND r6, r0, r3 ;apply significand mask to IEEE and save into r6 MOV pc, r14 ;return And here are the masks and number declarations so you can understand: IEEE DCD 0x40300000 ;2.75 decimal or 01000000001100000000000000000000 binary SMASK DCD 0x80000000 ;Sign bit mask EMASK DCD 0x7F800000 ;Exponent mask GMASK DCD 0x007FFFFF ;Significand mask When I step through with the debugger, the results I get are not what I expect after working through it on paper. EDIT: What I mean, is that after the subroutine runs, registers 4, 5, and 6 all remain 0. I can't figure out why the masks are not working. I think I do not fully understand how the number is being stored in the register or using the masks wrong. Any help appreciated. If you need more info just ask. EDIT: entry point: Very simple, just trying to get these subroutines working. ENTRY LDR r1, IEEE ;load IEEE num into r1 BL UnpackIEEE ;call unpack sub SWI SWI_Exit ;finish

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  • How to I convert a Silverlight 3.0 project to Silverlight 4.0?

    - by Justin
    I have a solution with several Silverlight Class Libraries and a Silverlight Application in it. I was originally built in VS 2008 with Silverlight 3.0. What changes do I need to make so that it builds using Silverlight 4.0? I already have VS 2010 and the Silverlight 4.0 toolkit installed. When I opened the project it seems to have upgraded to .NET 4.0 in my ASP.NET Web Project but not the Silverlight projects. Pretty sure they are still building against .NET 3.5 and Silverlight 3.0. Thanks.

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  • emacs23 pops up debugger way too frequently

    - by werner r.
    Since I've upgraded to Ubuntu lucid and emacs23, Emacs pops up the debugger in situations, where emacs22 does not. For example, when hitting C-c C-c in org-mode, emacs22 simply states can do nothing useful at this location, whereas in emacs23 the debugger shows up. Debugger entered--Lisp error: (error "C-c C-c can do nothing useful at this location") signal(error ("C-c C-c can do nothing useful at this location")) error("C-c C-c can do nothing useful at this location") org-ctrl-c-ctrl-c(nil) call-interactively(org-ctrl-c-ctrl-c nil nil) That only illustrates the pattern -- the behavior is not limited to org-mode. Occurring every 3 minutes, it really annoys me. How can I prevent it? I've already tried to stop this using debug-on-error and stack-trace-on-error: it didn't work.

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  • Error // Usage: rails new APP_PATH [options] // when running 'rails server'

    - by madphill
    Background info: I'm using GIT to get a repository of a project with Ruby files in it. The project lives in my SITES folder under home directory on my Mac. I have Ruby: 1.8.7 I have just upgraded Rails to: 3.0.3 All I am trying to accomplish is to be able to render localhost.com:3000 in my browser of the GIT project i've already downloaded so I can work on it locally. I ran the command 'rails server' and was returned the message below:: Usage: rails new APP_PATH [options] Options: [--skip-gemfile] # Don't create a Gemfile -m, [--template=TEMPLATE] # Path to an application template (can be a filesystem path or URL) -d, [--database=DATABASE] # Preconfigure for selected database (options: mysql/oracle/postgresql/sqlite3/frontbase/ibm_db) # Default: sqlite3 -O, [--skip-active-record] # Skip Active Record files -J, [--skip-prototype] # Skip Prototype files -T, [--skip-test-unit] # Skip Test::Unit files [--dev] # Setup the application with Gemfile pointing to your Rails checkout -r, [--ruby=PATH] # Path to the Ruby binary of your choice # Default: /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby -G, [--skip-git] # Skip Git ignores and keeps -b, [--builder=BUILDER] # Path to an application builder (can be a filesystem path or URL) [--edge] # Setup the application with Gemfile pointing to Rails repository Runtime options: -f, [--force] # Overwrite files that already exist -s, [--skip] # Skip files that already exist -p, [--pretend] # Run but do not make any changes -q, [--quiet] # Supress status output Rails options: -h, [--help] # Show this help message and quit -v, [--version] # Show Rails version number and quit Description: The 'rails new' command creates a new Rails application with a default directory structure and configuration at the path you specify. Example: rails new ~/Code/Ruby/weblog This generates a skeletal Rails installation in ~/Code/Ruby/weblog. See the README in the newly created application to get going.

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  • upgrading from MVC4 to MVC5 pre-Release

    - by Jack M
    I have made that dreadful error of upgrading from MVC4 to MVC5 pre-release by updating the razor, and mvc webpage in my references I have System.Web.Mvc, System.Web.Webpages, System.Web.Webpages.Razor and System.Web.Razor as version v4.0.30319, when I run my application I get [A]System.Web.WebPages.Razor.Configuration.HostSection cannot be cast to [B]System.Web.WebPages.Razor.Configuration.HostSection. Type A originates from 'System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' in the context 'Default' at location 'C:\Windows\Microsoft.Net\assembly\GAC_MSIL\System.Web.WebPages.Razor\v4.0_2.0.0.0__31bf3856ad364e35\System.Web.WebPages.Razor.dll'. Type B originates from 'System.Web.WebPages.Razor, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' in the context 'Default' at location 'C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files\membership\c70f06fe\9163b1ca\assembly\dl3\291c956e\73c25daa_cf74ce01\System.Web.WebPages.Razor.dll'. is this the same as http://www.asp.net/whitepapers/mvc4-release-notes Thanks Adding a stacktrace: [InvalidCastException: [A]System.Web.WebPages.Razor.Configuration.HostSection cannot be cast to [B]System.Web.WebPages.Razor.Configuration.HostSection. Type A originates from 'System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' in the context 'Default' at location 'C:\Windows\Microsoft.Net\assembly\GAC_MSIL\System.Web.WebPages.Razor\v4.0_2.0.0.0__31bf3856ad364e35\System.Web.WebPages.Razor.dll'. Type B originates from 'System.Web.WebPages.Razor, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' in the context 'Default' at location 'C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files\c70f06fe\9163b1ca\assembly\dl3\291c956e\73c25daa_cf74ce01\System.Web.WebPages.Razor.dll'.] System.Web.WebPages.Razor.WebRazorHostFactory.CreateHostFromConfig(String virtualPath, String physicalPath) +193 System.Web.WebPages.Razor.RazorBuildProvider.GetHostFromConfig() +51 System.Web.WebPages.Razor.RazorBuildProvider.CreateHost() +24 System.Web.WebPages.Razor.RazorBuildProvider.get_Host() +34 System.Web.WebPages.Razor.RazorBuildProvider.EnsureGeneratedCode() +85 System.Web.WebPages.Razor.RazorBuildProvider.get_CodeCompilerType() +34 System.Web.Compilation.BuildProvider.GetCompilerTypeFromBuildProvider(BuildProvider buildProvider) +189 System.Web.Compilation.BuildProvidersCompiler.ProcessBuildProviders() +265 System.Web.Compilation.BuildProvidersCompiler.PerformBuild() +21 System.Web.Compilation.BuildManager.CompileWebFile(VirtualPath virtualPath) +580 System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate) +571 System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate) +203 System.Web.Compilation.BuildManager.GetVirtualPathObjectFactory(VirtualPath virtualPath, HttpContext context, Boolean allowCrossApp, Boolean throwIfNotFound) +249 System.Web.Compilation.BuildManager.GetCompiledType(VirtualPath virtualPath) +17 System.Web.Mvc.BuildManagerCompiledView.Render(ViewContext viewContext, TextWriter writer) +90 System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context) +380 System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +109 System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +890 System.Web.Mvc.ControllerActionInvoker.InvokeActionResultWithFilters(ControllerContext controllerContext, IList`1 filters, ActionResult actionResult) +97 System.Web.Mvc.Async.<>c__DisplayClass1e.<BeginInvokeAction>b__1b(IAsyncResult asyncResult) +241 System.Web.Mvc.Controller.<BeginExecuteCore>b__1d(IAsyncResult asyncResult, ExecuteCoreState innerState) +29 System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +111 System.Web.Mvc.Controller.EndExecuteCore(IAsyncResult asyncResult) +53 System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +19 System.Web.Mvc.MvcHandler.<BeginProcessRequest>b__4(IAsyncResult asyncResult, ProcessRequestState innerState) +51 System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +111 System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +606 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +288

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  • Problem in DLL update in .Net

    - by Deepak
    My site stops working when I drop a new DLL in the bin of my virtual directory. It took to much time to work properly again. Sometimes I have to reset the IIS. Its happening since I upgraded my .Net framework from 1.1 to 3.1

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  • Unary NOT/Integersize of the architecture

    - by sid_com
    From "Mastering Perl/Chapter 16/Bit Operators/Unary NOT,~": The unary NOT operator (sometimes called the complement operator), ~, returns the bitwise negation, or 1's complement, of the value, based on integer size of the architecture Why does the following script output two different values? #!/usr/local/bin/perl use warnings; use 5.012; use Config; my $int_size = $Config{intsize} * 8; my $value = 0b1111_1111; my $complement = ~ $value; say length sprintf "%${int_size}b", $value; say length sprintf "%${int_size}b", $complement; Output: 32 64

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  • Why don't stacks grow upwards (for security)?

    - by AshleysBrain
    This is related to the question 'Why do stacks typically grow downwards?', but more from a security point of view. I'm generally referring to x86. It strikes me as odd that the stack would grow downwards, when buffers are usually written to upwards in memory. For example a typical C++ string has its end at a higher memory address than the beginning. This means that if there's a buffer overflow you're overwriting further up the call stack, which I understand is a security risk, since it opens the possibility of changing return addresses and local variable contents. If the stack grew upwards in memory, wouldn't buffer overflows simply run in to dead memory? Would this improve security? If so, why hasn't it been done? What about x64, do those stacks grow upwards and if not why not?

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  • Is there any .Net JIT Support from chip vendors?

    - by NoMoreZealots
    I know that ARM actually has some support for Java and SUN obviously, but I haven't really references seen any chip vendor supporting a .Net JIT compiler. I know IBM and Intel both support C compilers, as well as TI and many of the embedded chip vendors. When you think of it, all a JIT compiler is, is the last stages of compilation and optimization which you would think would be a good match for a chip vendor's expertize. Perhaps a standardized Plug In compilation engine for the VM would make sense. Microsoft is targeting .Net to embedded Windows platforms as well, so they are fair game. Pete

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  • Android strict dependency checks in SDK 17

    - by Christine
    This is not a question because I already found the answer. The new Android SDK 17 has a stricter dependency check on jar files. At the same time, they added a jar that I think wasn't there before. My project encountered a conflict between the new annotations.jar in the SDK and one that I already used. Replacing one by the other would work, if they have the same origin. My annotations.jar is from jetbrains, via a Guice dependency, so replacing it doesn't work. This is the error I got: [2012-03-22 10:54:27 - MyApp] Jar mismatch! Fix your dependencies [2012-03-22 10:54:46 - MyApp] Found 2 versions of annotations.jar in the dependency list, [2012-03-22 10:54:46 - MyApp] but not all the versions are identical (check is based on SHA-1 only at this time). [2012-03-22 10:54:46 - MyApp] All versions of the libraries must be the same at this time. [2012-03-22 10:54:46 - MyApp] Versions found are: [2012-03-22 10:54:46 - MyApp] Path: /opt/android-sdk-linux_x86/tools/support/annotations.jar [2012-03-22 10:54:46 - MyApp] Length: 1463 [2012-03-22 10:54:46 - MyApp] SHA-1: 6f59fa3a223df6f332bee8b8bffb526f7445018b [2012-03-22 10:54:46 - MyApp] Path: /home/christine/workspace/MyApp/libs/annotations.jar [2012-03-22 10:54:46 - MyApp] Length: 7593 [2012-03-22 10:54:46 - MyApp] SHA-1: e28fe9e70610beb9ef49226a9e56fed7a86e742a [2012-03-22 10:54:46 - MyApp] Jar mismatch! Fix your dependencies

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  • What is the preferred way to update database schemas in multiple production environments

    - by rmarimon
    I am about to install some 20 servers with the same web application in multiple locations connected to their own local database. I will be updating the web applications remotely (perhaps using debian's package manager) and I'm sure will eventually need to update the database schemas. Since each server could be eventually be using a different release of the web application, I need a way to apply the incremental changes to the servers. I'm thinking something like this. Let's start with database.schema.1 as the original release of the database and assume this number increases with each new version of the schema. I eventually could end up with database.schema.17 as the current release. For a new installation this would be the schema to install. It seems to me that I would need consecutive translations like database.translation.1.2 which would convert database.schema.1 into database.schema.2, database.translation.2.3 to convert from 2 to 3 and so on until 17. It seems that whenever I change a schema I need to alter the database but perhaps I need to run some script to update the data which might be done with SQL but might require an external non sql script. What is the appropriate way to organize all these files? What is the automatic way to apply those upgrades to the schema? Where do I store the current version number of the schema?

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