Re: [ck] Re: [announce] [patch] Voluntary Kernel Preemption Patch

André Goddard Rosa
2004-07-11T17:29:58Z

Hi, can anyone explain this:

Using Ingo's first patch when I:
echo 1 > /proc/sys/kernel/kernel_preempt

my system hang up after 2 seconds aproximately.

Using Ingo's modifications + Con's it doesn't lock anymore

and is the best kernel that I have used to test..

Thanks!

On Sun, 11 Jul 2004 16:38:53 +0200, Ingo Molnar <mingo@elte.hu> wrote:
>
>
>
> * Con Kolivas <kernel@kolivas.org> wrote:
>
> > Ok I've done one better than that ;) I had wli help make some
> > instrumentation for me to help find the remaining non preemptible
> > kernel portions and set the cutoff to 2ms. Here is what I found:
> >
> > 7ms non-preemptible critical section violated 2 ms preempt threshold
> > starting at reiserfs_sync_fs+0x2d/0xc2 and ending at reiser
> > fs_lookup+0xe2/0x221
> >
> > 9ms non-preemptible critical section violated 2 ms preempt threshold
> > starting at reiserfs_dirty_inode+0x37/0x10e and ending at r
> > eiserfs_dirty_inode+0xb0/0x10e
> >
> > These seem to be the two offenders. Hope this helps.
>
> great!
>
> meanwhile i spent an afternoon with another latency testing suite:
>
> http://www.alsa-project.org/~iwai/latencytest-0.5.3.tar.gz
>
> it was reporting more accurate latencies, except that there were strange
> spikes of latencies. It turned out that for whatever reason, userspace
> RDTSC is not always reliable on my box (!).
>
> I've attached two fixes against latencytest - one makes rdtsc timestamps
> more reliable, the other one fixes an SMP bug in the kernel module (it
> would lock up under SMP otherwise.).
>
> here's a latencytest QuickStart: 'cd latencytest; make', then
> 'insmod kernel/latency-test.ko', then 'cd tests; ../bin/run_tests'.
>
> Assuming you have RTC and audio enabled in your kernel it should work
> fine. It produces PNGs in the same format as Benno's latencytest suite.
>
> Ingo
>
>
>

--
[]s,

André