Re: [PATCH] block: use nanosecond resolution for iostat

[Omar Sandoval <osandov@osandov.com>]

On Fri, Sep 21, 2018 at 08:27:17PM -0600, Jens Axboe wrote:
> On 9/21/18 5:44 PM, Omar Sandoval wrote:
> > From: Omar Sandoval <osandov@fb.com>
> > 
> > Klaus Kusche reported that the I/O busy time in /proc/diskstats was not
> > updating properly on 4.18. This is because we started using ktime to
> > track elapsed time, and we convert nanoseconds to jiffies when we update
> > the partition counter. However, this gets rounded down, so any I/Os that
> > take less than a jiffy are not accounted for. Previously in this case,
> > the value of jiffies would sometimes increment while we were doing I/O,
> > so at least some I/Os were accounted for.
> > 
> > Let's convert the stats to use nanoseconds internally. We still report
> > milliseconds as before, now more accurately than ever. The value is
> > still truncated to 32 bits for backwards compatibility.
> 
> Thanks Omar, applied for 4.19.

Thanks, Jens. I also just pushed a regression test to blktests.