linux-kernel - Re: [PATCH] small optimization to update_curr

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Message-ID: <20081031134606.GA12193@sgi.com>
Date:	Fri, 31 Oct 2008 08:46:06 -0500
From:	Dimitri Sivanich <sivanich@....com>
To:	Steven Noonan <steven@...inklabs.net>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] small optimization to update_curr_rt

On Fri, Oct 31, 2008 at 06:10:13AM -0700, Steven Noonan wrote:
> On Fri, Oct 31, 2008 at 6:03 AM, Dimitri Sivanich <sivanich@....com> wrote:
> > A very minor improvement, but might it be better to check sched_rt_runtime(rt_rq)
> > before taking the rt_runtime_lock?
> 
> Is it possible that the attribute sched_rt_runtime is checking could
> change by the time it acquires the lock? If not, should be fine, I
> think.
>

Steve,

While it might be possible for it to change in that instant, I don't know if it matters.

If the runtime value should change to RUNTIME_INF in that instant, it will be caught in sched_rt_runtime_exceeded().  If it changed from RUNTIME_INF to a lower value, I doubt it would matter much, as at most one more rt_rq value wouldn't be checked.  Either way some rt_rq values would have been checked during the loop and some would not.
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