Message-ID: <1406567993.2411.31.camel@j-VirtualBox>
Subject: Re: [PATCH -tip/master 3/7] locking/mcs: Remove obsolete comment
From: Jason Low <jason.low2@hp.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Davidlohr Bueso <davidlohr@hp.com>, mingo@kernel.org, aswin@hp.com,
        linux-kernel@vger.kernel.org
Date: Mon, 28 Jul 2014 10:19:53 -0700
In-Reply-To: <20140728165733.GU19379@twins.programming.kicks-ass.net>
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On Mon, 2014-07-28 at 18:57 +0200, Peter Zijlstra wrote:
> On Mon, Jul 28, 2014 at 09:53:58AM -0700, Davidlohr Bueso wrote:
> > Well, it's not hard to see where the contention is when working on
> > locking issues with perf. With mutexes there are only two sources,
> > either the task is just spinning trying to get the lock, or its gone to
> > the slowpath, and you can see a lot of contention on the wait_lock. 
> > 
> > So unless I'm missing something, I don't think we'd need to make this
> > noinline again -- although I forget why it was changed in the first
> > place.
> 
> Not to mention that there's no actual caller of this function in the
> entire kernel ;-) Currently its just 'documentation' describing what an
> actual MCS lock looks like.

Yeah, we only use the cancellable version of the lock anyway and there's
currently no benefit of changing the regular mcs lock to noinline.

I was mainly thinking it could be helpful in potential later uses of the
regular mcs lock (if anyone comes up with a need to use it) where it
might not be as obvious where the contention is occurring.

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