linux-kernel - Re: [RFC PATCH 1/2] percpu_counter: Allow falling back to global counter on large system

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Message-ID: <alpine.DEB.2.20.1603172058190.18714@east.gentwo.org>
Date:	Thu, 17 Mar 2016 20:58:46 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Waiman Long <waiman.long@....com>
cc:	Tejun Heo <tj@...nel.org>, Dave Chinner <dchinner@...hat.com>,
	xfs@....sgi.com, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Scott J Norton <scott.norton@...com>,
	Douglas Hatch <doug.hatch@...com>
Subject: Re: [RFC PATCH 1/2] percpu_counter: Allow falling back to global
 counter on large system

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?