On Fri, Mar 25, 2022 at 02:57:14PM +0100, Claudio Fontana wrote: > On 3/25/22 2:54 PM, Daniel P. Berrangé wrote: > > 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 > > INFO? DEBUG? Or nothing at all? Thanks again I think DEBUG is sufficient for any logging in this code. 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 :|
