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

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Date:	Thu, 7 Apr 2016 17:38:54 -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 2/3] percpu_stats: Simple per-cpu statistics count helper
 functions

On 04/07/2016 04:41 PM, Tejun Heo wrote:
> 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.
>

In this case, I think I will drop this reset functionality. It is not 
really needed for this patchset.

Thanks for the feedback!

Cheers,
Longman