Hi, a bit of an early ping on this, just wondering if the general direction of the changes seems ok. Thanks, Claudio On 3/21/22 9:13 AM, 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(); > + int rv = fcntl(fd, F_SETPIPE_SZ, pipe_sz); > + > + if (rv < 0) { > + VIR_ERROR(_("failed to set pipe size to %d (errno=%d)"), pipe_sz, errno); > + return -1; > + } > + VIR_INFO("fd %d pipe size adjusted to %d", fd, rv); > + return 0; > +} > + > +#else /* !__linux__ */ > +static int virFileWrapperSetPipeSize(int fd) > +{ > + return 0; > +} > +#endif /* !__linux__ */ > + > + > /** > * virFileWrapperFdNew: > * @fd: pointer to fd to wrap > @@ -282,6 +347,10 @@ 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")); > + } > + > if (output) { > virCommandSetInputFD(ret->cmd, pipefd[0]); > virCommandSetOutputFD(ret->cmd, fd); >
