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_...@crudebyte.com Message-ID of version with performance benchmark (v4): cover.1579567019.git.qemu_...@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