linux-kernel - Re: [RFC for-6.2/block V2] block: Change the granularity of io ticks from ms to ns

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Date:   Thu, 8 Dec 2022 00:35:55 +0000
From:   Keith Busch <kbusch@...nel.org>
To:     Chaitanya Kulkarni <chaitanyak@...dia.com>
Cc:     Jens Axboe <axboe@...nel.dk>,
        Gulam Mohamed <gulam.mohamed@...cle.com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "philipp.reisner@...bit.com" <philipp.reisner@...bit.com>,
        "lars.ellenberg@...bit.com" <lars.ellenberg@...bit.com>,
        "christoph.boehmwalder@...bit.com" <christoph.boehmwalder@...bit.com>,
        "minchan@...nel.org" <minchan@...nel.org>,
        "ngupta@...are.org" <ngupta@...are.org>,
        "senozhatsky@...omium.org" <senozhatsky@...omium.org>,
        "colyli@...e.de" <colyli@...e.de>,
        "kent.overstreet@...il.com" <kent.overstreet@...il.com>,
        "agk@...hat.com" <agk@...hat.com>,
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        "junxiao.bi@...cle.com" <junxiao.bi@...cle.com>,
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        "konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
        "joe.jin@...cle.com" <joe.jin@...cle.com>
Subject: Re: [RFC for-6.2/block V2] block: Change the granularity of io ticks
 from ms to ns

On Wed, Dec 07, 2022 at 11:17:12PM +0000, Chaitanya Kulkarni wrote:
> On 12/7/22 15:08, Jens Axboe wrote:
> > 
> > My default peak testing runs at 122M IOPS. That's also the peak IOPS of
> > the devices combined, and with iostats disabled. If I enabled iostats,
> > then the performance drops to 112M IOPS. It's no longer device limited,
> > that's a drop of about 8.2%.
> > 
> 
> Wow, clearly not acceptable that's exactly I asked for perf
> numbers :).

For the record, we did say per-io ktime_get() has a measurable
performance harm and should be aggregated.

  https://www.spinics.net/lists/linux-block/msg89937.html