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. v7->v8: * Split previous patch 3 into two patches [patch 3], [patch 4]. * Error out if a 9p2000.u client sends a Treaddir request, likewise error out if a 9p2000.L client sends a Tread request on a directory [patch 6]. Unchanged patches: [patch 1], [patch 2], [patch 5], [patch 7]. Message-ID of previous version (v7): cover.1595166227.git.qemu_...@crudebyte.com Message-ID of version with performance benchmark (v4): cover.1579567019.git.qemu_...@crudebyte.com Christian Schoenebeck (7): tests/virtio-9p: added split readdir tests 9pfs: make v9fs_readdir_response_size() public 9pfs: split out fs driver core of v9fs_co_readdir() 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 | 159 ++++++++++++++-------------- 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, 434 insertions(+), 94 deletions(-) -- 2.20.1