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

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Message-ID: <20180802061146.GA48671@dennisz-mbp.dhcp.thefacebook.com>
Date:   Wed, 1 Aug 2018 23:11:48 -0700
From:   Dennis Zhou <dennisszhou@...il.com>
To:     Tejun Heo <tj@...nel.org>
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

Hi Tejun,

On Wed, Aug 01, 2018 at 09:10:11AM -0700, Tejun Heo wrote:
> 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?
> 

Yeah, that makes sense. I've renamed it to lat_avg and updated the
Documentation file as well.

Thanks,
Dennis