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Subject: Re: [patch] CFS scheduler, -v19
From: Ian Kent <raven@themaw.net>
To: Ingo Molnar <mingo@elte.hu>
Cc: Chuck Ebbert <cebbert@redhat.com>, Bill Davidsen <davidsen@tmr.com>,
       linux-kernel@vger.kernel.org,
       Linus Torvalds <torvalds@linux-foundation.org>
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Date: Tue, 17 Jul 2007 13:01:14 +0800
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On Mon, 2007-07-16 at 23:55 +0200, Ingo Molnar wrote:
> * Chuck Ebbert <cebbert@redhat.com> wrote:
> 
> > On 07/13/2007 05:19 PM, Bill Davidsen wrote:
> > > 
> > > I should really go back to 2.6.21.6, 2.6.22 has many bizarre behaviors
> > > with FC6. Automount starts taking 30% of CPU (unused at the moment)
> > 
> > Can you confirm whether CFS is involved, i.e. does it spin like that 
> > even without the CFS patch applied?
> 
> hmmm .... could you take out the kernel/time.c (sys_time()) changes from 
> the CFS patch, does that solve the automount issue? If yes, could 
> someone take a look at automount and check whether it makes use of 
> time(2) and whether it combines it with finer grained time sources?

Yes it does and I have two reported bugs so far.

In several places I have code similar to:

wait.tv_sec = time(NULL) + 1;
wait.tv_nsec = 0;

signaled = 0;
while (!signaled) {
        status = pthread_cond_timedwait(&cond, &mutex, &wait);
       if (status) {
             if (status == ETIMEDOUT)
                  break;
             fatal(status);
      }
}

lead to automount spinning with strace output a bit like:

futex(0x80034b60, FUTEX_WAKE, 1)  = 0
clock_gettime(CLOCK_REALTIME, {1184593936, 130925919}) = 0
time(NULL)                        = 1184593935
futex(0x80034b60, FUTEX_WAKE, 1)  = 0
clock_gettime(CLOCK_REALTIME, {1184593936, 131160876}) = 0
time(NULL)                        = 1184593935
futex(0x80034b60, FUTEX_WAKE, 1)  = 0
clock_gettime(CLOCK_REALTIME, {1184593936, 131377080}) = 0
time(NULL)                        = 1184593935
futex(0x80034b60, FUTEX_WAKE, 1)  = 0
clock_gettime(CLOCK_REALTIME, {1184593936, 131593297}) = 0
time(NULL)                        = 1184593935
futex(0x80034b60, FUTEX_WAKE, 1)  = 0
clock_gettime(CLOCK_REALTIME, {1184593936, 131871792}) = 0

There should be something like:

futex(0x5555557868c4, FUTEX_WAIT, 5321099, {0, 998091311}) = -1 ETIMEDOUT (Connection timed out)

in there I think.

Ian