On 06/20/2016 09:19 AM, Denis V. Lunev wrote: > From: Evgeny Yakovlev <eyakov...@virtuozzo.com> > > Some guests (win2008 server for example) do a lot of unnecessary > flushing when underlying media has not changed. This adds additional > overhead on host when calling fsync/fdatasync. > > This change introduces a dirty flag in BlockDriverState which is set > in bdrv_set_dirty and is checked in bdrv_co_flush. This allows us to > avoid unnessesary flushing when storage is clean.
s/unnessesary/unnecessary/ > > The problem with excessive flushing was found by a performance test > which does parallel directory tree creation (from 2 processes). > Results improved from 0.424 loops/sec to 0.432 loops/sec. > Each loop creates 10^3 directories with 10 files in each. > > Signed-off-by: Evgeny Yakovlev <eyakov...@virtuozzo.com> > Signed-off-by: Denis V. Lunev <d...@openvz.org> > CC: Kevin Wolf <kw...@redhat.com> > CC: Max Reitz <mre...@redhat.com> > CC: Stefan Hajnoczi <stefa...@redhat.com> > CC: Fam Zheng <f...@redhat.com> > --- > block.c | 1 + > block/dirty-bitmap.c | 3 +++ > block/io.c | 6 ++++++ > include/block/block_int.h | 1 + > 4 files changed, 11 insertions(+) Otherwise seems reasonable, but I'll let others with more experience on flush semantics chime in. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
signature.asc
Description: OpenPGP digital signature
