Re: Help understanding slow down

Jakob Oestergaard
2004-05-24T10:43:35Z

On Mon, May 24, 2004 at 05:59:36PM +1000, Nick Piggin wrote:
> Phy Prabab wrote:
> >NO HT, disabled in bios and did not enable in kernel:
> >cat /proc/cpuinfo|grep processor|wc -l
> > 2
> >grep SMT .config (2.6.7-rc1)
> ># CONFIG_SCHED_SMT is not set
> >
> >On 2.4.21 I also include "append=noht"
> >
>
> OK good, that makes things simpler.
>
> I'm out of ideas though. The kernel just doesn't seem to be
> the problem here. Can you put together a testcase that causes
> the problem and that we can download and reproduce it?

You could try running your program with 'strace -T' to see which system
calls are causing the slowdown.

If you make a lot of system calls, this can be a little tedious to go
thru though... But it should reveal to you where your program is
waiting.

Note; if you use gprof and compile with the '-pg' switch, the profiler
will show you a profile of CPU time, not wall-clock time. Your
performance problem is wall-clock time, and if your program actually
spends a lot of time waiting in some system call, this will *NOT* show
up in a normal gprof profile.

/ jakob