On 3/25/22 11:41 AM, Daniel P. Berrangé wrote: > On Mon, Mar 21, 2022 at 09:13:20AM +0100, Claudio Fontana wrote: >> virsh save is very slow with a default pipe size, so set a larger one. >> >> This change improves throughput by ~400% on fast nvme or ramdisk, >> for the current only user of virFileWrapperFdNew: the qemu driver. >> >> Best value currently measured is 1MB, which happens to be also >> the kernel default for the pipe-max-size. >> >> We do not try to use a pipe buffer larger than what the setting >> of /proc/sys/fs/pipe-max-size currently allows. >> >> Signed-off-by: Claudio Fontana <cfontana@xxxxxxx> >> --- >> src/util/virfile.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 69 insertions(+) >> >> see v1 at >> https://listman.redhat.com/archives/libvir-list/2022-March/229252.html >> >> Changes v1 -> v2: >> >> * removed VIR_FILE_WRAPPER_BIG_PIPE, made the new pipe resizing >> unconditional (Michal) >> >> * moved code to separate functions (Michal) >> >> * removed ternary op, disliked in libvirt (Michal) >> >> * added #ifdef __linux__ (Ani Sinha) >> >> * try smallest value between currently best measured value (1MB) >> and the pipe-max-size setting. If pipe-max-size cannot be read, >> try kernel default max (1MB). (Daniel) >> >> >> >> diff --git a/src/util/virfile.c b/src/util/virfile.c >> index a04f888e06..13bdd42c68 100644 >> --- a/src/util/virfile.c >> +++ b/src/util/virfile.c >> @@ -201,6 +201,71 @@ struct _virFileWrapperFd { >> }; >> >> #ifndef WIN32 >> + >> +#ifdef __linux__ >> +/** >> + * virFileWrapperGetBestPipeSize: >> + * >> + * get the best pipe size to use with virFileWrapper. >> + * >> + * We first check the maximum we are allowed by the system pipe-max-size, >> + * and then use the minimum between that and our tested best value. >> + * This is because a request beyond pipe-max-size may fail with EPERM. >> + * If we are unable to read pipe-max-size, use the kernel default (1MB). >> + * >> + * Return value is the pipe size to use. >> + */ >> + >> +static int virFileWrapperGetBestPipeSize(void) >> +{ >> + const char path[] = "/proc/sys/fs/pipe-max-size"; >> + int best_sz = 1024 * 1024; /* good virsh save results with this size */ >> + int max_sz; >> + >> + if (virFileReadValueInt(&max_sz, path) < 0) { >> + max_sz = 1024 * 1024; /* this is the kernel default pipe-max-size */ >> + VIR_WARN("failed to read %s, trying default %d", path, max_sz); >> + } else if (max_sz > best_sz) { >> + max_sz = best_sz; >> + } >> + return max_sz; >> +} >> + >> +/** >> + * virFileWrapperSetPipeSize: >> + * @fd: the fd of the pipe >> + * >> + * Set best pipe size on the passed file descriptor for bulk transfers of data. >> + * >> + * default pipe size (usually 64K) is generally not suited for large transfers >> + * to fast devices. This has been measured to improve virsh save by 400% >> + * in ideal conditions. >> + * >> + * Return value is 0 on success, -1 and errno set on error. >> + * OS note: only for linux, on other OS this is a no-op. >> + */ >> +static int >> +virFileWrapperSetPipeSize(int fd) >> +{ >> + int pipe_sz = virFileWrapperGetBestPipeSize(); > > I wonder if we shouldn't just ignore the proc setting and instead > > for (sz = 1024 * 1024 ; sz >= 64 * 1024; sz /= 2) { > int rv = fcntl(fd, F_SETPIPE_SZ, sz); > if (rv < 0 && errno == EPERM) { > continue; > } > if (rv < 0) { > virReportError(...) > return -1; > } > > VIR_INFO("fd %d pipe size adjusted to %d", fd, sz); > return 0; > } > > > We'll only have 1 loop iteration in the default case, and 4 iterations > in the worst case, and gracefully leave it on the default if the last > ieratino fails > > With regards, > Daniel > Yes, seems better to me, Claudio
