On Fri, Mar 25, 2022 at 02:52:05PM +0100, Claudio Fontana wrote: > On 3/25/22 2:13 PM, Daniel P. Berrangé wrote: > > On Fri, Mar 25, 2022 at 01:54:51PM +0100, Claudio Fontana wrote: > >> currently the only user of virFileWrapperFdNew is the qemu driver; > >> virsh save is very slow with a default pipe size. > >> This change improves throughput by ~400% on fast nvme or ramdisk. > >> > >> Best value currently measured is 1MB, which happens to be also > >> the kernel default for the pipe-max-size. > >> > >> Signed-off-by: Claudio Fontana <cfontana@xxxxxxx> > >> --- > >> > >> see v2 at > >> https://listman.redhat.com/archives/libvir-list/2022-March/229423.html > >> > >> Changes v2 -> v3: > >> > >> * removed reading of max-pipe-size from procfs, > >> instead make multiple attempts on EPERM with smaller sizes. > >> In the regular case, this should succeed on the first try. > >> (Daniel) > >> > >> 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) > >> > >> > >> src/util/virfile.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++ > >> 1 file changed, 49 insertions(+) > >> > >> diff --git a/src/util/virfile.c b/src/util/virfile.c > >> index a04f888e06..876b865974 100644 > >> --- a/src/util/virfile.c > >> +++ b/src/util/virfile.c > >> @@ -201,6 +201,51 @@ struct _virFileWrapperFd { > >> }; > >> > >> #ifndef WIN32 > >> + > >> +#ifdef __linux__ > >> + > >> +/** > >> + * 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. A value of 1MB has been measured to improve virsh save > >> + * by 400% in ideal conditions. We retry multiple times with smaller sizes > >> + * on EPERM to account for possible small values of /proc/sys/fs/pipe-max-size. > >> + * > >> + * 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 sz; > >> + > >> + for (sz = 1024 * 1024; sz >= 64 * 1024; sz /= 2) { > >> + int rv = fcntl(fd, F_SETPIPE_SZ, sz); > >> + if (rv < 0 && errno == EPERM) { > >> + continue; /* retry with half the size */ > >> + } > >> + if (rv < 0) { > >> + break; > >> + } > >> + VIR_INFO("fd %d pipe size adjusted to %d", fd, sz); > >> + return 0; > >> + } > >> + VIR_WARN("failed to set pipe size to %d (errno=%d)", sz, errno); > >> + return -1; > >> +} > >> + > >> +#else /* !__linux__ */ > >> +static int virFileWrapperSetPipeSize(int fd) > >> +{ > >> + return 0; > >> +} > >> +#endif /* !__linux__ */ > >> + > >> + > >> /** > >> * virFileWrapperFdNew: > >> * @fd: pointer to fd to wrap > >> @@ -282,6 +327,10 @@ virFileWrapperFdNew(int *fd, const char *name, unsigned int flags) > >> > >> ret->cmd = virCommandNewArgList(iohelper_path, name, NULL); > >> > >> + if (virFileWrapperSetPipeSize(pipefd[!output]) < 0) { > >> + virReportError(VIR_ERR_SYSTEM_ERROR, "%s", _("unable to set pipe size, data transfer might be slow")); > > > > Push this into virFileWrapperSetPipeSize instead of the VIR_WARN > > there, and use virReportSystemError passing in the errno value too. > > > ok, what about also warning on EPERM? In the normal case we should succeed on the first try I think. We generally try to avoid any VIR_WARN in cases that we expect to be still functional. Users tend to complain when they get warnings for these kind of things. I think coping with smaller max size is a normal situation, so its merely a perf factor, not a functional problem. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
