On 06/14/2016 09:25 AM, Denis V. Lunev wrote: > With a bdrv_co_write_zeroes method on a target BDS zeroes will not be placed > into the wire. Thus the target could be very efficiently zeroed out. This > is should be done with the largest chunk possible. > > This improves the performance of the live migration of the empty disk by > 150 times if NBD supports write_zeroes. > > Signed-off-by: Denis V. Lunev <d...@openvz.org> > Reviewed-by: Vladimir Sementsov-Ogievskiy<vsement...@virtuozzo.com> > CC: Stefan Hajnoczi <stefa...@redhat.com> > CC: Fam Zheng <f...@redhat.com> > CC: Kevin Wolf <kw...@redhat.com> > CC: Max Reitz <mre...@redhat.com> > CC: Jeff Cody <jc...@redhat.com> > CC: Eric Blake <ebl...@redhat.com> > --- > block/mirror.c | 32 +++++++++++++++++++++++++++++++- > 1 file changed, 31 insertions(+), 1 deletion(-) > > diff --git a/block/mirror.c b/block/mirror.c > index c7b3639..c2f8773 100644 > --- a/block/mirror.c > +++ b/block/mirror.c > @@ -21,6 +21,7 @@ > #include "qemu/ratelimit.h" > #include "qemu/bitmap.h" > > +#define MIRROR_ZERO_CHUNK (3u << (29 - BDRV_SECTOR_BITS)) /* 1.5 Gb */
Probably nicer to track this in bytes. And do you really want a hard-coded arbitrary limit, or is it better to live with MIN_NON_ZERO(target_bs->bl.max_pwrite_zeroes, INT_MAX)? > @@ -512,7 +513,8 @@ static int mirror_dirty_init(MirrorBlockJob *s) > > end = s->bdev_length / BDRV_SECTOR_SIZE; > > - if (base == NULL && !bdrv_has_zero_init(target_bs)) { > + if (base == NULL && !bdrv_has_zero_init(target_bs) && > + target_bs->drv->bdrv_co_write_zeroes == NULL) { Indentation is off, although if checkpatch.pl doesn't complain I guess it doesn't matter that much. Why should you care whether the target_bs->drv implements a callback? Can't you just rely on the normal bdrv_*() functions to do the dirty work of picking the most efficient implementation without you having to bypass the block layer? In fact, isn't that the whole goal of bdrv_make_zero() - why not call that instead of reimplementing it? Patch needs rebasing - we've redone this into bdrv_co_pwrite_zeroes and a byte interface, since upstream commit c1499a5e. > bdrv_set_dirty_bitmap(s->dirty_bitmap, 0, end); > return 0; > } > @@ -546,6 +548,34 @@ static int mirror_dirty_init(MirrorBlockJob *s) > } > sector_num += n; > } > + > + if (base != NULL || bdrv_has_zero_init(target_bs)) { You're now repeating the conditional that used to be 'bool mark_all_dirty' (well, this is !mark_all_dirty); is it worth keeping the simpler bool around? > + /* no need to zero out entire disk */ > + return 0; > + } > + > + for (sector_num = 0; sector_num < end; ) { > + int nb_sectors = MIN(MIRROR_ZERO_CHUNK, end - sector_num); Why limit yourself to 1.5G? It's either too small for what you can really do, or too large for what the device permits. See my above comment about MIN_NON_ZERO. > + int64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME); > + > + if (now - last_pause_ns > SLICE_TIME) { > + last_pause_ns = now; > + block_job_sleep_ns(&s->common, QEMU_CLOCK_REALTIME, 0); > + } > + > + if (block_job_is_cancelled(&s->common)) { > + return -EINTR; > + } > + > + if (s->in_flight == MAX_IN_FLIGHT) { > + trace_mirror_yield(s, s->in_flight, s->buf_free_count, -1); > + mirror_wait_for_io(s); > + continue; > + } Hmm - I guess your mirror yield points are why you couldn't just directly use bdrv_make_zero(); but is that something where some code refactoring can share more code rather than duplicating it? > + > + mirror_do_zero_or_discard(s, sector_num, nb_sectors, false); > + sector_num += nb_sectors; > + } > return 0; > } > > -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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