[Libguestfs] [PATCH libnbd v2 1/3] fuse: Enable multithread support

This was much simpler than I though, merely changing fuse_loop -> fuse_loop_mt. FUSE itself will call our operations in parallel, so we have to be careful about shared state. Testing with fio shows this is about the same or a tiny bit slower than before, which is not that surprising -- we are using the synchronous API. It should be possible to improve performance either by issuing commands in parallel on the same handle (complicated) or by using multi-conn. test.fio contains: [global] filename=test.img bs=4k direct=1 rw=read [job1] [job2] [job3] [job4] Run the test: $ touch test.img $ nbdfuse test.img [ nbdkit memory 1G ] & $ fio test.fio $ fusermount3 -u test.img Without this patch: READ: bw=239MiB/s (250MB/s), 59.6MiB/s-59.7MiB/s (62.5MB/s-62.6MB/s), io=4096MiB (4295MB), run=17166-17167msec With this patch: READ: bw=237MiB/s (248MB/s), 59.2MiB/s-59.2MiB/s (62.0MB/s-62.1MB/s), io=4096MiB (4295MB), run=17303-17310msec --- fuse/nbdfuse.c | 6 +++++- fuse/operations.c | 7 +++++++ 2 files changed, 12 insertions(+), 1 deletion(-) diff --git a/fuse/nbdfuse.c b/fuse/nbdfuse.c index 3deef75..fa35080 100644 --- a/fuse/nbdfuse.c +++ b/fuse/nbdfuse.c @@ -151,6 +151,7 @@ main (int argc, char *argv[]) int64_t ssize; const char *s; struct fuse_args fuse_args = FUSE_ARGS_INIT (0, NULL); + struct fuse_loop_config fuse_loop_config; FILE *fp; for (;;) { @@ -475,7 +476,10 @@ main (int argc, char *argv[]) } /* Enter the main loop. */ - r = fuse_loop (fuse); + memset (&fuse_loop_config, 0, sizeof fuse_loop_config); + fuse_loop_config.clone_fd = 0; + fuse_loop_config.max_idle_threads = 10; + r = fuse_loop_mt (fuse, &fuse_loop_config); if (r < 0) { errno = -r; perror ("fuse_loop"); diff --git a/fuse/operations.c b/fuse/operations.c index 2c38c6e..4da701e 100644 --- a/fuse/operations.c +++ b/fuse/operations.c @@ -16,6 +16,13 @@ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ +/* FUSE operations invoked by the kernel. + * + * Note these may be called in parallel from multiple threads, so any + * shared state needs to be read-only or else protected by mutexes. + * libnbd calls are OK. + */ + #include <config.h> #include <stdio.h> -- 2.31.1