linux-kernel - Re: [PATCH 0/3] sched: newidle and RT wake-buddy fixes

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Date:	Mon, 30 Jun 2008 11:01:44 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Gregory Haskins <ghaskins@...ell.com>
cc:	Ingo Molnar <mingo@...e.hu>, peterz@...radead.org, npiggin@...e.de,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: [PATCH 0/3] sched: newidle and RT wake-buddy fixes


On Mon, 30 Jun 2008, Gregory Haskins wrote:

>
> >>> On Mon, Jun 30, 2008 at  9:15 AM, in message <20080630131511.GA7506@...e.hu>,
> Ingo Molnar <mingo@...e.hu> wrote:
>
> > * Gregory Haskins <ghaskins@...ell.com> wrote:
> >
> >> Hi Ingo,
> >>   The following patches apply to linux-tip/sched/devel and enhance the
> >> performance of the kernel (specifically in PREEMPT_RT, though they do
> >> not regress mainline performance as far as I can tell).  They offer
> >> somewhere between 50-100% speedups in netperf performance, depending
> >> on the test.
> >
> > -tip testing found this boot hang:
>
> Ok, I dug in a little bit here.  I haven't verified this out yet, but I think the problem is that
> your config is PREEMPT_VOLUNTARY which NOPs the preempt_disable() in schedule() that
> I rely on to allow the lock to be dropped.  (Doh!)

This means that there's a location somewhere that does a cond_resched?
Perhaps we should look to see what does that. And perhaps the
preempt_disable should not be allowing PREEMPT_VOLUNTARY to do scheduling
with cond_resched.

-- Steve

>
> One way I can fix this is to fixup the newidle() code to only play the irq dropping tricks
> ifdef CONFIG_PREEMPT == TRUE.  Does this sound reasonable, or is there a better way
> to address this?

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