What do the different times mean when using UNIX's "time" command?
- by fluffels
When I time a program on Ubuntu 10.4 I get output like:
real 0m14.581s
user 0m14.570s
sys 0m0.010s
What do these different categories mean?
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Why do debug symbols so adversely affect the performance of threaded applications on Linux?
- by fluffels
Hi. I'm writing a ray tracer. Recently, I added threading to the program to exploit the additional cores on my i5 Quad Core. In a weird turn of events the debug version of the application is now running slower, but the optimized build is running faster than before I added threading. I'm passing the "-g -pg" flags to gcc for the debug build and the "-O3" flag for the optimized build. Host system: Ubuntu Linux 10.4 AMD64. I know that debug symbols add significant overhead to the program, but the relative performance has always been maintained. I.e. a faster algorithm will always run faster in both debug and optimization builds. Any idea why I'm seeing this behavior?Read the article
