linux-kernel - Re: [rfc 19/45] cpu alloc: NFS statistics

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Message-ID: <20071121005307.GA26793@Krystal>
Date:	Tue, 20 Nov 2007 19:53:08 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Trond Myklebust <trond.myklebust@....uio.no>
Cc:	Christoph Lameter <clameter@....com>, ak@...e.de,
	akpm@...ux-foundation.org, travis@....com,
	linux-kernel@...r.kernel.org
Subject: Re: [rfc 19/45] cpu alloc: NFS statistics

* Trond Myklebust (trond.myklebust@....uio.no) wrote:
> 
> On Tue, 2007-11-20 at 16:50 -0500, Mathieu Desnoyers wrote:
> > Then my original point is valid : put_no_resched() will cause unwanted
> > scheduler latencies. It's designed only to be used from within the
> > scheduler code itself. The correct approach would be a standard
> > put_cpu().
> > 
> > Or am I missing something ?
> 
> Then someone who cares about scheduler latency had better audit the code
> and figure out which calls are made under spinlock, and which aren't:
> it's not on my personal list of high priorities. I'll be happy to review
> any patches, though.
> 

put_cpu() will work flawlessly when nested within a spinlock. the
spinlock disabled itself preemption, and a nested preemption
disable/enable/check will end up incrementing/decrementing the preempt
cours. The check at the end will just not call the scheduler when nested
within a spinlock.

If this is what you are worried about, then you shouldn't. I am a bit
surprised about your reaction though.. so I probably missed
something/don't understand correctly your fear about check_resched
within a spinlock.

Mathieu

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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