Re: [PATCH] block: add iostat counters for flush requests

[Darrick J. Wong]

On Thu, Nov 21, 2019 at 08:56:14AM -0700, Jens Axboe wrote:
> On 11/21/19 3:40 AM, Konstantin Khlebnikov wrote:
> > Requests that triggers flushing volatile writeback cache to disk (barriers)
> > have significant effect to overall performance.
> > 
> > Block layer has sophisticated engine for combining several flush requests
> > into one. But there is no statistics for actual flushes executed by disk.
> > Requests which trigger flushes usually are barriers - zero-size writes.
> > 
> > This patch adds two iostat counters into /sys/class/block/$dev/stat and
> > /proc/diskstats - count of completed flush requests and their total time.
> 
> This makes sense to me, and the "recent" discard addition already proved
> that we're fine extending with more fields. Unless folks object, I'd be
> happy to queue this up for 5.5.

Looks like a good addition to /me... :)

--D

> -- 
> Jens Axboe
>