Re: [PATCH v2 0/7] 9pfs: Twalk optimization

[Christian Schoenebeck <qemu_oss@crudebyte.com>]

On Freitag, 4. Juni 2021 18:31:28 CEST Greg Kurz wrote:
> On Fri, 4 Jun 2021 17:48:49 +0200
> 
> Christian Schoenebeck <qemu_oss@crudebyte.com> wrote:
> > This patch set reduces latency of Twalk handling by reducing the amount of
> > thread hops, similar to previous Treaddir optimization.
> > 
> > The performance gain of this patch set is not as spectacular as previously
> > with Treaddir, but there is definitely a measurable difference.
> > 
> > The actualy performance optimization is patch 7. With the benchmark of
> > patch 2, the runtime of the Twalk test was cut in half. In real world
> > tests
> > I measured a performance gain (i.e. running an entire guest OS, and hence
> > mixed with all other kinds of 9p requests) of about 2%, again measured in
> > a
> > mix, not concentrated on Twalk alone.
> > 
> > v1 -> v2:
> >   * Added a separate [NEW PATCH 1] for fixing not_same_qid() semantic.
> 
> Strangely, patch 1 appears between patch 3 and 4 in my email client.

My bad, I forgot to take care about the time stamps of the individual patches 
this time.

> >   * Code style: use sizeof(var-name) instead of sizeof(type-name)
> >   
> >     [PATCH 3].
> >   
> >   * Split out dropping fid_to_qid() into separate [PATCH 4].
> >   
> >   * Split out replacing not_same_qid() by same_stat_id() into separate
> >   
> >     [PATCH 5].
> >   
> >   * Split out dropping root_qid into separate [PATCH 6].
> 
> I could have a look at all the patches except the last one. LGTM.
> You can add my R-b for patches 1 and 3 to 6.
> 
> Reviewed-by: Greg Kurz <groug@kaod.org>

Queued patches 1, 3..6 on 9p.next:

https://github.com/cschoenebeck/qemu/commits/9p.next

Thanks!

> I'll try to find some time for patch 7 next week.
> 

Twalk can be tricky, so no hurry! It takes what it takes.

> > Christian Schoenebeck (7):
> >   9pfs: fix not_same_qid()
> >   9pfs: Twalk benchmark
> >   9pfs: capture root stat
> >   9pfs: drop fid_to_qid()
> >   9pfs: replace not_same_qid() by same_stat_id()
> >   9pfs: drop root_qid
> >   9pfs: reduce latency of Twalk
> >  
> >  hw/9pfs/9p.c                 | 128 +++++++++++++++++++++++------------
> >  hw/9pfs/9p.h                 |   2 +-
> >  tests/qtest/virtio-9p-test.c |  30 ++++++++
> >  3 files changed, 116 insertions(+), 44 deletions(-)

Best regards,
Christian Schoenebeck