From: Christian Schoenebeck <qemu_oss@crudebyte.com>
To: qemu-devel@nongnu.org
Cc: Greg Kurz <groug@kaod.org>
Subject: [PATCH v5 0/6] 9pfs: readdir optimization
Date: Thu, 26 Mar 2020 22:28:25 +0100 [thread overview]
Message-ID: <cover.1585258105.git.qemu_oss@crudebyte.com> (raw)
As previously mentioned, I was investigating performance issues with 9pfs.
Raw file read/write of 9pfs is actually quite good, provided that client
picked a reasonable high msize (maximum message size). I would recommend
to log a warning on 9p server side if a client attached with a small msize
that would cause performance issues for that reason.
However there are other aspects where 9pfs currently performs suboptimally,
especially readdir handling of 9pfs is extremely slow, a simple readdir
request of a guest typically blocks for several hundred milliseconds or
even several seconds, no matter how powerful the underlying hardware is.
The reason for this performance issue: latency.
Currently 9pfs is heavily dispatching a T_readdir request numerous times
between main I/O thread and a background I/O thread back and forth; in fact
it is actually hopping between threads even multiple times for every single
directory entry during T_readdir request handling which leads in total to
huge latencies for a single T_readdir request.
This patch series aims to address this severe performance issue of 9pfs
T_readdir request handling. The actual performance optimization is patch 5.
v4->v5:
* Rebased to master (SHA-1 762fa6d7).
* Dropped benchmark patches (see v4 if you want to run a benchmark on v5).
* Divided split-readdir test into 3 individual tests, which also fixes the
previously discussed transport error [patch 1].
* Fixed English spelling for 'split' [patch 1].
* Rename max_count -> maxsize [NEW patch 2].
* Divided previous huge readdir optimization patch into individual patches
[patch 3], [patch 4], [patch 5].
* Added comment on v9fs_readdir_response_size() [patch 3].
* Renamed v9fs_co_readdir_lowlat() -> v9fs_co_readdir_many() [patch 4].
* Adjusted comment on v9fs_co_readdir_many() [patch 4].
* Added comment on v9fs_co_run_in_worker() [NEW patch 6].
* Adjusted commit log message of several patches.
Message-ID of previous version (v4):
cover.1579567019.git.qemu_oss@crudebyte.com
Christian Schoenebeck (6):
tests/virtio-9p: added split readdir tests
9pfs readdir: rename max_count -> maxsize
9pfs: make v9fs_readdir_response_size() public
9pfs: add new function v9fs_co_readdir_many()
9pfs: T_readdir latency optimization
9pfs: clarify latency of v9fs_co_run_in_worker()
hw/9pfs/9p.c | 148 ++++++++++++++--------------
hw/9pfs/9p.h | 23 +++++
hw/9pfs/codir.c | 181 ++++++++++++++++++++++++++++++++---
hw/9pfs/coth.h | 15 ++-
tests/qtest/virtio-9p-test.c | 108 +++++++++++++++++++++
5 files changed, 386 insertions(+), 89 deletions(-)
--
2.20.1
next reply other threads:[~2020-03-26 22:32 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-26 21:28 Christian Schoenebeck [this message]
2020-03-26 21:24 ` [PATCH v5 1/6] tests/virtio-9p: added split readdir tests Christian Schoenebeck
2020-03-26 21:24 ` [PATCH v5 2/6] 9pfs readdir: rename max_count -> maxsize Christian Schoenebeck
2020-03-26 21:24 ` [PATCH v5 3/6] 9pfs: make v9fs_readdir_response_size() public Christian Schoenebeck
2020-03-26 21:25 ` [PATCH v5 4/6] 9pfs: add new function v9fs_co_readdir_many() Christian Schoenebeck
2020-03-26 21:25 ` [PATCH v5 5/6] 9pfs: T_readdir latency optimization Christian Schoenebeck
2020-03-26 21:25 ` [PATCH v5 6/6] 9pfs: clarify latency of v9fs_co_run_in_worker() Christian Schoenebeck
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