linux-ext4 - Re: [PATCH v2 2/4] percpu_stats: Enable 64-bit counts in 32-bit architectures

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Date:	Tue, 12 Apr 2016 14:15:22 -0400
From:	Waiman Long <waiman.long@....com>
To:	Tejun Heo <tj@...nel.org>
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

On 04/11/2016 06:17 PM, Tejun Heo wrote:
> 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.
>

I have updated my patch to use percpu_counter instead. Thanks for all 
the comments and review so far.

Cheers,
Longman
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