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Re: [RFC PATCH 1/2] percpu_counter: Allow falling back to global counter

To: Waiman Long <waiman.long@xxxxxxx>
Subject: Re: [RFC PATCH 1/2] percpu_counter: Allow falling back to global counter on large system
From: Christoph Lameter <cl@xxxxxxxxx>
Date: Thu, 17 Mar 2016 20:58:46 -0500 (CDT)
Cc: Tejun Heo <tj@xxxxxxxxxx>, Dave Chinner <dchinner@xxxxxxxxxx>, xfs@xxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Ingo Molnar <mingo@xxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Scott J Norton <scott.norton@xxxxxx>, Douglas Hatch <doug.hatch@xxxxxx>
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References: <1457146299-1601-1-git-send-email-Waiman.Long@xxxxxxx> <1457146299-1601-2-git-send-email-Waiman.Long@xxxxxxx> <alpine.DEB.2.20.1603071220470.1453@xxxxxxxxxxxxxxx> <56E9B219.7090500@xxxxxxx>
On Wed, 16 Mar 2016, Waiman Long wrote:

> > If the cpumask is empty you can use the global count. Otherwise you just
> > need to add up the counters of the cpus set in the cpumask.
> >
>
> I have modified the patch to try that out. However, that doesn't yield that
> much of improvement in term of performance and it slows down the percpu fast
> path a bit. So I am going to focus on my existing patch first and think about
> that later.

Hmmm... Maybe look at the cause of the slowdown first?

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