05.08.2019 14:49, Max Reitz wrote: > In write-blocking mode, all writes to the top node directly go to the > target. We must only mirror chunks of data that are aligned to the > job's granularity, because that is how the dirty bitmap works. > Therefore, the request alignment for writes must be the job's > granularity (in write-blocking mode). > > Unfortunately, this forces all reads and writes to have the same > granularity (we only need this alignment for writes to the target, not > the source), but that is something to be fixed another time. > > Signed-off-by: Max Reitz <[email protected]> > --- > This is an alternative to Vladimir's "util/hbitmap: fix unaligned reset" > patch. I don't mind much either way, both of pros and cons. Comparing > this patch to Vladimir's: > > + Makes copy-mode=write-blocking really work (unless I'm mistaken) > - Lowers performance with copy-mode=write-blocking unnecessarily > --- > block/mirror.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/block/mirror.c b/block/mirror.c > index 8cb75fb409..3f9c5a178a 100644 > --- a/block/mirror.c > +++ b/block/mirror.c > @@ -1481,6 +1481,15 @@ static void > bdrv_mirror_top_child_perm(BlockDriverState *bs, BdrvChild *c, > *nshared = BLK_PERM_ALL; > } > > +static void bdrv_mirror_top_refresh_limits(BlockDriverState *bs, Error > **errp) > +{ > + MirrorBDSOpaque *s = bs->opaque; > + > + if (s && s->job && s->job->copy_mode == MIRROR_COPY_MODE_WRITE_BLOCKING) > { > + bs->bl.request_alignment = s->job->granularity; > + } > +} > + > /* Dummy node that provides consistent read to its users without requiring > it > * from its backing file and that allows writes on the backing file chain. > */ > static BlockDriver bdrv_mirror_top = { > @@ -1493,6 +1502,7 @@ static BlockDriver bdrv_mirror_top = { > .bdrv_co_block_status = bdrv_co_block_status_from_backing, > .bdrv_refresh_filename = bdrv_mirror_top_refresh_filename, > .bdrv_child_perm = bdrv_mirror_top_child_perm, > + .bdrv_refresh_limits = bdrv_mirror_top_refresh_limits, > }; > > static BlockJob *mirror_start_job( > @@ -1678,6 +1688,8 @@ static BlockJob *mirror_start_job( > > QTAILQ_INIT(&s->ops_in_flight); > > + bdrv_refresh_limits(mirror_top_bs, &error_abort); > + > trace_mirror_start(bs, s, opaque); > job_start(&s->common.job); > >
Am I right that the fact that no guest request will skip this limit is guaranteed by aio_context_acquire/release around blockdev_mirror_common? Not sure how much it lowers performance, but it should work.. Reviewed-by: Vladimir Sementsov-Ogievskiy <[email protected]> -- Best regards, Vladimir
