linux-kernel - Re: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper functions

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Date:	Thu, 7 Apr 2016 16:41:14 -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 2/3] percpu_stats: Simple per-cpu statistics count helper
 functions

Hello, Waiman.

On Thu, Apr 07, 2016 at 04:37:06PM -0400, Waiman Long wrote:
> I would say that because I am lazy, I don't want compute the deltas every
> time I want to see the effect of running a certain type of workload on the
> statistics counts. I have use case that I need to track 10 or so statistics
> counts and monitor their changes after running a job. It is much more
> convenient to do a reset and see what you get than doing manual subtractions
> to find out.

I don't know.  Write a simple script?  Even if you wanna keep it in
kernel, you can just have a base counter which offsets the summed up
value on read.

> I had taken a look at percpu-refcount.[ch]. I think the synchronization code
> is a bit overkill for this purpose as no one really need a very precise
> statistics counts nor precise atomic reset. I would prefer providing an
> optional atomic reset feature with slower statistics count update path for
> the time being. If we come across a use case where we need atomic reset with
> negligible slowdown, we could then refactor the code to use something
> similar to  what the percpu-refcount code is doing.

Please either drop reset or make it actually work; otherwise, I don't
think this should go in.

Thanks.

-- 
tejun