linux-kernel - Re: [PATCH 5/5] sched,futex: Provide delayed wakeup list

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Date:	Sat, 23 Nov 2013 21:25:40 -0800
From:	Davidlohr Bueso <davidlohr@...com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	dvhart@...ux.intel.com, tglx@...utronix.de, efault@....de,
	jeffm@...e.com, torvalds@...ux-foundation.org, scott.norton@...com,
	tom.vaden@...com, aswin@...com, Waiman.Long@...com,
	jason.low2@...com
Subject: Re: [PATCH 5/5] sched,futex: Provide delayed wakeup list

On Sat, 2013-11-23 at 13:01 +0100, Peter Zijlstra wrote:
> > I used to have a patch to schedule() that would always immediately fall
> > through and only actually block on the second call; it illustrated the
> > problem really well, in fact so well the kernels fails to boot most
> > times.
> 
> I found the below on my filesystem -- making it apply shouldn't be hard.
> Making it work is the same effort as that patch you sent, we need to
> guarantee all schedule() callers can deal with not actually sleeping --
> aka. spurious wakeups.

Thanks, I'll definitely try the patch and see what comes up.

> 
> I don't think anybody ever got that thing to run reliable enough to see
> if the idea proposed in the patch made any difference to actual
> workloads though.

Since your idea can also be applied to sysv sems (patch 3/3 back then),
I can definitely do some Oracle runs which IIRC, also likes doing
multiple wakeups at once. In any case this patch deals very nicely with
our customer workload, which is why I believe its particularly good
here.

Thanks,
Davidlohr

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