Re: [RFC -v3 PATCH 2/3] sched: add yield_to function

From: Avi Kivity
Date: Wed Jan 05 2011 - 03:36:09 EST

On 01/05/2011 04:39 AM, KOSAKI Motohiro wrote:
> On 01/04/2011 08:14 AM, KOSAKI Motohiro wrote:
> > Also, If pthread_cond_signal() call sys_yield_to imlicitly, we can
> > avoid almost Nehalem (and other P2P cache arch) lock unfairness
> > problem. (probaby creating pthread_condattr_setautoyield_np or similar
> > knob is good one)
> Often, the thread calling pthread_cond_signal() wants to continue
> executing, not yield.

Then, it doesn't work.

After calling pthread_cond_signal(), T1 which cond_signal caller and T2
which waked start to GIL grab race. But usually T1 is always win because
lock variable is in T1's cpu cache. Why kernel and userland have so much
different result? One of a reason is glibc doesn't have any ticket lock scheme.

If you are interesting GIL mess and issue, please feel free to ask more.

I suggest looking into an explicit round-robin scheme, where each thread adds itself to a queue and an unlock wakes up the first waiter.

error compiling committee.c: too many arguments to function

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