linux-kernel - Re: [PATCH v6 4/6] locking/pvqspinlock: Collect slowpath lock statistics

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Message-ID: <20150911231355.GD19736@linux-q0g1.site>
Date:	Fri, 11 Sep 2015 16:13:55 -0700
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Waiman Long <Waiman.Long@....com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Scott J Norton <scott.norton@...com>,
	Douglas Hatch <doug.hatch@...com>
Subject: Re: [PATCH v6 4/6] locking/pvqspinlock: Collect slowpath lock
 statistics

On Fri, 11 Sep 2015, Waiman Long wrote:

>A sample of statistics counts after system bootup (with vCPU
>overcommit) was:
>
>hash_hops_count=9001
>kick_latencies=138047878
>kick_unlock_count=9001
>kick_wait_count=9000
>spurious_wakeup=3
>wait_again_count=2
>wait_head_count=10
>wait_node_count=8994
>wake_latencies=713195944

Any reason you chose not to make the stats per-cpu? The locking
numbers don't have to be exact, so you can easily get away with
it and suffer from much less overhead that resorting to atomics.
Obviously assuming that reading/collecting the stats is done
infrequently, such as between workloads or at bootup as you did.

Thanks,
Davidlohr
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