On 06/24/2016 09:06 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 unnesessary flushing when storage is clean.
s/unnesessary/unnecessary/ (I pointed this out against v2 https://lists.gnu.org/archive/html/qemu-devel/2016-06/msg05817.html, which makes me wonder if anything else was missed) > > 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> > CC: John Snow <js...@redhat.com> > --- > +++ b/include/block/block_int.h > @@ -418,6 +418,8 @@ struct BlockDriverState { > int sg; /* if true, the device is a /dev/sg* */ > int copy_on_read; /* if true, copy read backing sectors into image > note this is a reference count */ > + > + bool dirty; > bool probed; > Conflicts with the current state of Kevin's block branch (due to my reordering and conversion of bool parameters); so you'll want to rebase. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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