Date: Sat, 28 Sep 2013 21:13:39 +0200
From: Andi Kleen <andi@firstfloor.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ingo Molnar <mingo@kernel.org>, Waiman Long <Waiman.Long@hp.com>,
        Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Rik van Riel <riel@redhat.com>,
        Peter Hurley <peter@hurleysoftware.com>,
        Davidlohr Bueso <davidlohr.bueso@hp.com>,
        Alex Shi <alex.shi@intel.com>, Tim Chen <tim.c.chen@linux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Matthew R Wilcox <matthew.r.wilcox@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Michel Lespinasse <walken@google.com>,
        Andi Kleen <andi@firstfloor.org>,
        "Chandramouleeswaran, Aswin" <aswin@hp.com>,
        "Norton, Scott J" <scott.norton@hp.com>
Subject: Re: [PATCH] rwsem: reduce spinlock contention in wakeup code path
Message-ID: <20130928191339.GP18242@two.firstfloor.org>
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> Of course, since then, we may well have screwed things up and now we
> sleep under it, but I still really think it was a mistake to do it in
> the first place.
> 
> So if the primary reason for this is really just that f*cking anon_vma
> lock, then I would seriously suggest:
> 
>  - turn it back into a spinlock (or rwlock_t, since we subsequently
> separated the read and write paths)

Yes please. spinlocks/rwlocks have so much nicer performance behavior than
rwsems/mutexes (which noone seems to fully understand)

We had also significant performance regressions from every such
spinning->sleeping change in the VM (this was just the latest)

And afaik anon_vma is usually hold short.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only.
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