linux-kernel - Re: [RFC PATCH] blk-iocost: Optimize the ioc_refreash

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Message-ID: <9d1098dc-f716-872b-ea63-aea4a44355dc@linux.alibaba.com>
Date:   Fri, 4 Dec 2020 11:36:19 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     axboe@...nel.dk, baolin.wang7@...il.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] blk-iocost: Optimize the ioc_refreash_vrate()
 function



在 2020/12/3 4:32, Tejun Heo 写道:
> On Sun, Nov 29, 2020 at 10:37:18AM +0800, Baolin Wang wrote:
>> The ioc_refreash_vrate() will only be called in ioc_timer_fn() after
>> starting a new period or stopping the period.
>>
>> So when starting a new period, the variable 'pleft' in ioc_refreash_vrate()
>> is always the period's time, which means if the abs(ioc->vtime_err)
>> is less than the period's time, the vcomp is 0, and we do not need
>> compensate the vtime_rate in this case, just set it as the base vrate
>> and return.
>>
>> When stopping the period, the ioc->vtime_err will be cleared to 0,
>> and we also do not need to compensate the vtime_rate, just set it as
>> the base vrate and return.
> 
> Before, the function did something which is conceptually discrete and
> describable. After, its operation is intertwined with when it's called. I
> don't think this sort of micro optimizations are beneficial in cold paths.

OK. I understood your concern. Thanks for your input.