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

[Greg Kurz]

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.

>   * 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>

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

> 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(-)
>