linux-kernel - Re: [PATCH v2 2/4] percpu_stats: Enable 64-bit counts in 32-bit architectures

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Date:	Mon, 11 Apr 2016 18:17:00 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Waiman Long <waiman.long@....com>
Cc:	Theodore Ts'o <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Christoph Lameter <cl@...ux.com>, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Scott J Norton <scott.norton@....com>,
	Douglas Hatch <doug.hatch@....com>,
	Toshimitsu Kani <toshi.kani@....com>
Subject: Re: [PATCH v2 2/4] percpu_stats: Enable 64-bit counts in 32-bit
 architectures

Hello, Waiman.

On Fri, Apr 08, 2016 at 02:45:38PM -0400, Waiman Long wrote:
> The percpu_stats construct allows minimal overhead in maintaining statistics
> counts. The percpu_counter construct, on the other hand, has a higher
> performance overhead and a bit more complex to set up and tear down when

If you're referring to the preemption on/off, as I wrote before, we'll
probably be able to improve that with this_cpu_add_return so that the
only extra overhead is an easily predictable branch which is extremely
cheap.  It's better to improve common constructs anyway.

> more than one statistics counts are needed. In fact, my first draft of the

And yeah, it can be cumbersome to set up and tear down multiple
percpu_counters.  If there are enough consumers, we can extend
percpu_counter to handle multiple counters, right?

Thanks.

-- 
tejun