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Date: Fri, 4 Sep 2015 09:55:42 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Waiman Long <Waiman.Long@hp.com>, Ingo Molnar <mingo@kernel.org>
Subject: Re: [4.2, Regression] Queued spinlocks cause major XFS performance
 regression
Message-ID: <20150904075542.GB18489@twins.programming.kicks-ass.net>
References: <20150904054820.GY3902@dastard>
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On Fri, Sep 04, 2015 at 05:11:43PM +1000, Dave Chinner wrote:
> $ grep PARAVIRT .config
> CONFIG_PARAVIRT=y
> # CONFIG_PARAVIRT_DEBUG is not set
> # CONFIG_PARAVIRT_SPINLOCKS is not set
> CONFIG_PARAVIRT_TIME_ACCOUNTING=y
> CONFIG_PARAVIRT_CLOCK=y
> $

Curious, with PARAVIRT_SPINLOCKS=n we _should_ end up in
virt_queued_spin_lock() which is a simple test-and-set lock, much like
the lock debugging code should end up being.