linux-kernel - Re: [PATCH v2] block: make iolatency avg

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Message-ID: <20180801161011.GS1206094@devbig004.ftw2.facebook.com>
Date:   Wed, 1 Aug 2018 09:10:11 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Dennis Zhou <dennisszhou@...il.com>
Cc:     Jens Axboe <axboe@...nel.dk>, Josef Bacik <jbacik@...com>,
        kernel-team@...com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH v2] block: make iolatency avg_lat exponentially decay

On Wed, Aug 01, 2018 at 08:49:58AM -0700, Tejun Heo wrote:
> Hello,
> 
> On Tue, Jul 31, 2018 at 05:25:59PM -0700, Dennis Zhou wrote:
> ...
> > +	/*
> > +	 * CALC_LOAD takes in a number stored in fixed point representation.
> > +	 * Because we are using this for IO time in ns, the values stored
> > +	 * are significantly larger than the FIXED_1 denominator (2048).
> > +	 * Therefore, rounding errors in the calculation are negligible and
> > +	 * can be ignored.
> > +	 */
> > +	exp_idx = min_t(int, BLKIOLATENCY_NR_EXP_FACTORS - 1,
> > +			iolat->cur_win_nsec / BLKIOLATENCY_EXP_BUCKET_SIZE);
> 
> Build bot is complaining about naked 64bit div.  Should use one of the
> div64*() helpers.
> 
> Looks good to me.  Once Johannes's concerns are addressed, please feel
> free to add

Ooh, one nitpick.  total_lat_avg is a bit of a misnomer now.  Maybe
rename to lat_avg?

Thanks.

-- 
tejun