Message-ID: <1437959674.25997.30.camel@stgolabs.net>
Subject: Re: [PATCH v3 3/7] locking/pvqspinlock: Collect slowpath lock
 statistics
From: Davidlohr Bueso <dave@stgolabs.net>
To: Waiman Long <Waiman.Long@hp.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        Scott J Norton <scott.norton@hp.com>,
        Douglas Hatch <doug.hatch@hp.com>
Date: Sun, 26 Jul 2015 18:14:34 -0700
In-Reply-To: <1437595962-21472-4-git-send-email-Waiman.Long@hp.com>
References: <1437595962-21472-1-git-send-email-Waiman.Long@hp.com>
	 <1437595962-21472-4-git-send-email-Waiman.Long@hp.com>
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On Wed, 2015-07-22 at 16:12 -0400, Waiman Long wrote:
> This patch enables the accumulation of kicking and waiting related
> PV qspinlock statistics when the new QUEUED_LOCK_STAT configuration
> option is selected. It also enables the collection of kicking and
> wakeup latencies which have a heavy dependency on the CPUs being used.
> 
> The measured latencies for different CPUs are:
> 
> 	CPU		Wakeup		Kicking
> 	---		------		-------
> 	Haswell-EX	89.8us		 7.4us
> 	Westmere-EX	67.6us		 9.3us
> 

But you don't mention anything about the overhead of enabling
QUEUED_LOCK_STAT. This does several atomic ops, thus potentially
thrashing workloads.

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