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[PATCH v7 0/6] 9pfs: readdir optimization
From: |
Christian Schoenebeck |
Subject: |
[PATCH v7 0/6] 9pfs: readdir optimization |
Date: |
Sun, 19 Jul 2020 15:43:47 +0200 |
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 4.
v6->v7:
* Rebased to master: SHA-1 b442119329
* Handle directory seeking more consistently by doing it in
do_readdir_many() instead of in v9fs_readdir() [patch 3], [patch 4].
* Updated API doc on v9fs_co_readdir_many(): make it clear that
v9fs_free_dirents() must always be called, including error cases
[patch 3].
* New patch: use different lock type for 9p2000.u vs. 9p2000.L
[patch 5].
Unchanged patches: [patch 1], [patch 2], [patch 6].
Message-ID of previous version (v6):
cover.1587309014.git.qemu_oss@crudebyte.com
Message-ID of version with performance benchmark (v4):
cover.1579567019.git.qemu_oss@crudebyte.com
Christian Schoenebeck (6):
tests/virtio-9p: added split readdir tests
9pfs: make v9fs_readdir_response_size() public
9pfs: add new function v9fs_co_readdir_many()
9pfs: T_readdir latency optimization
9pfs: differentiate readdir lock between 9P2000.u vs. 9P2000.L
9pfs: clarify latency of v9fs_co_run_in_worker()
hw/9pfs/9p.c | 144 ++++++++++++-------------
hw/9pfs/9p.h | 50 ++++++++-
hw/9pfs/codir.c | 196 +++++++++++++++++++++++++++++++++--
hw/9pfs/coth.h | 15 ++-
tests/qtest/virtio-9p-test.c | 108 +++++++++++++++++++
5 files changed, 419 insertions(+), 94 deletions(-)
--
2.20.1
- [PATCH v7 0/6] 9pfs: readdir optimization,
Christian Schoenebeck <=
[PATCH v7 1/6] tests/virtio-9p: added split readdir tests, Christian Schoenebeck, 2020/07/19
[PATCH v7 6/6] 9pfs: clarify latency of v9fs_co_run_in_worker(), Christian Schoenebeck, 2020/07/19
[PATCH v7 4/6] 9pfs: T_readdir latency optimization, Christian Schoenebeck, 2020/07/19
[PATCH v7 5/6] 9pfs: differentiate readdir lock between 9P2000.u vs. 9P2000.L, Christian Schoenebeck, 2020/07/19