lkml.org 
[lkml]   [2015]   [Apr]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] blk: clean up plug
On Fri, Apr 17, 2015 at 04:54:40PM -0400, Jeff Moyer wrote:
> Shaohua Li <shli@fb.com> writes:
>
> > Current code looks like inner plug gets flushed with a
> > blk_finish_plug(). Actually it's a nop. All requests/callbacks are added
> > to current->plug, while only outmost plug is assigned to current->plug.
> > So inner plug always has empty request/callback list, which makes
> > blk_flush_plug_list() a nop. This tries to make the code more clear.
> >
> > Signed-off-by: Shaohua Li <shli@fb.com>
>
> Hi, Shaohua,
>
> I agree that this looks like a clean-up with no behavioral change, and
> it looks good to me. However,it does make me scratch my head about the
> numbers I was seeing. Here's the table from that other email thread[1]:
>
> device| vanilla | patch1 | dio-noplug | noflush-nested
> ------+------------+----------------+---------------+-----------------
> rssda | 701,684 | 1,168,527 | 1,342,177 | 1,297,612
> | 100% | +66% | +91% | +85%
> vdb0 | 358,264 | 902,913 | 906,850 | 922,327
> | 100% | +152% | +153% | +157%
>
> Patch1 refers to the first patch in this series, which fixes the merge
> logic for single-queue blk-mq devices. Each column after that includes
> that first patch. In dio-noplug, I removed the blk_plug from the
> direct-io code path (so there is no nesting at all). This is a control,
> since it is what I expect the outcome of the noflush-nested column to
> actually be. Then, the noflush-nested column leaves the blk_plug in
> place in the dio code, but includes the patch that prevents nested
> blk_plug's from being flushed. All numbers are the average of 5 runs.
> With the exception of the vanilla run on rssda (the first run was
> faster, causing the average to go up), the standard deviation is very
> small.
>
> For the dio-noplug column, if the inner plug really was a noop, then why
> would we see any change in performance? Like I said, I agree with your
> reading of the code and the patch. Color me confused. I'll poke at it
> more next week. For now, I think your patch is fine.
>
> Reviewed-by: Jeff Moyer <jmoyer@redhat.com>

Thanks! I don't know why either the your second makes change.

> Also, Jens or Shaohua or anyone, please review my blk-mq plug fix (patch
> 1/2 of aforementioned thread). ;)

You are not alone :), I posted 2 times too
http://marc.info/?l=linux-kernel&m=142627559617005&w=2


Thanks,
Shaohua


\
 
 \ /
  Last update: 2015-04-17 23:41    [W:0.042 / U:3.364 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site