Hi Christian, It seems that there was an issue with the posting of these series. Threading is inexistant. All the emails appear scattered and unsorted in my mailbox, between 12/16 and 12/18... which is a bit painful. I'll try to find some time to have a look anyway, but this greatly lowers the odds for these series to get multiple reviews, which seems problematic given the ** NOTE: ** section you've added to the cover. Please fix this.
Cheers, -- Greg On Wed, 18 Dec 2019 00:11:10 +0100 Christian Schoenebeck <qemu_...@crudebyte.com> wrote: > 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 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 fix is patch 8. I also > provided a convenient benchmark for comparing the performance improvements > by using the 9pfs "synth" driver (see patch 6 for instructions how to run > the benchmark), so no guest OS installation is required to peform this > benchmark A/B comparison. With patch 8 I achieved a performance improvement > of factor 40 on my test machine. > > ** NOTE: ** These patches are not heavily tested yet, nor thouroughly > reviewed for potential security issues yet. I decided to post them already > though, because I won't have the time in the next few weeks for polishing > them. The benchmark results should demonstrate though that it is worth the > hassle. So any testing/reviews/fixes appreciated! > > Christian Schoenebeck (9): > tests/virtio-9p: v9fs_string_read() didn't terminate string > 9pfs: validate count sent by client with T_readdir > hw/9pfs/9p-synth: added directory for readdir test > tests/virtio-9p: added READDIR test > tests/virtio-9p: check file names of READDIR response > 9pfs: READDIR benchmark > hw/9pfs/9p-synth: avoid n-square issue in synth_readdir() > 9pfs: T_readdir latency optimization > hw/9pfs/9p.c: benchmark time on T_readdir request > > hw/9pfs/9p-synth.c | 46 ++++++++++- > hw/9pfs/9p-synth.h | 5 ++ > hw/9pfs/9p.c | 150 ++++++++++++++++++--------------- > hw/9pfs/9p.h | 23 ++++++ > hw/9pfs/codir.c | 183 ++++++++++++++++++++++++++++++++++++++--- > hw/9pfs/coth.h | 3 + > tests/virtio-9p-test.c | 182 +++++++++++++++++++++++++++++++++++++++- > 7 files changed, 509 insertions(+), 83 deletions(-) >
