On Mon, Mar 28, 2022 at 01:06:03PM +0200, Michal Prívozník wrote: > On 3/25/22 16:10, 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> > > --- > > src/util/virfile.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 46 insertions(+) > > > > see v2 at > > https://listman.redhat.com/archives/libvir-list/2022-March/229423.html > > > > Changes v3 -> v4: > > > > * changed INFO and WARN messages to DEBUG (Daniel) > > > > 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) > > > > > > diff --git a/src/util/virfile.c b/src/util/virfile.c > > index a04f888e06..87539be0b9 100644 > > --- a/src/util/virfile.c > > +++ b/src/util/virfile.c > > @@ -201,6 +201,50 @@ 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. > > + * > > + * OS note: only for linux, on other OS this is a no-op. > > + */ > > +static void > > +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) { > > + VIR_DEBUG("EPERM trying to set fd %d pipe size to %d", fd, sz); > > + continue; /* retry with half the size */ > > + } > > + if (rv < 0) { > > + break; > > + } > > + VIR_DEBUG("fd %d pipe size adjusted to %d", fd, sz); > > + return; > > + } > > + virReportSystemError(errno, "%s", _("unable to set pipe size, data transfer might be slow")); > > This should have been VIR_WARN(). It's weird to report an error when the > function returns void. Actually I said to report an error in prvious version, as I figured we were handling the expect EPERM, but I guess we could even fail the last 64 KB iteration and stick with the default. So we need a slight tweak: static void 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) { VIR_DEBUG("EPERM trying to set fd %d pipe size to %d", fd, sz); continue; /* retry with half the size */ } if (rv < 0) { virReportSystemError(errno, "%s", _("unable to set pipe size")); return -1; } VIR_DEBUG("fd %d pipe size adjusted to %d", fd, sz); return 0; } VIR_WARN("Could set pipe size to 64 KB, leaving on default size"); return 0; } then the caller can treat -1 as fatal 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 :|
