Re: [Qemu-devel] [PATCH v2] migration/block: Avoid invoking blk_drain too frequently

[Juan Quintela <quintela@redhat.com>]

Fam Zheng <famz@redhat.com> wrote:
> On Wed, 03/15 17:31, Dr. David Alan Gilbert wrote:
>> * Fam Zheng (famz@redhat.com) wrote:
>> > On Wed, 03/15 11:37, Lidong Chen wrote:
>> > > Increase bmds->cur_dirty after submit io, so reduce the frequency
>> > > involve into blk_drain, and improve the performance obviously
>> > > when block migration.
>> > > 
>> > > The performance test result of this patch:
>> > > 
>> > > During the block dirty save phase, this patch improve guest os IOPS
>> > > from 4.0K to 9.5K. and improve the migration speed from
>> > > 505856 rsec/s to 855756 rsec/s.
>> > > 
>> > > Signed-off-by: Lidong Chen <jemmy858585@gmail.com>
>> > > ---
>> > >  migration/block.c | 3 +++
>> > >  1 file changed, 3 insertions(+)
>> > > 
>> > > diff --git a/migration/block.c b/migration/block.c
>> > > index 6741228..7734ff7 100644
>> > > --- a/migration/block.c
>> > > +++ b/migration/block.c
>> > > @@ -576,6 +576,9 @@ static int mig_save_device_dirty(QEMUFile *f, BlkMigDevState *bmds,
>> > >              }
>> > >  
>> > >              bdrv_reset_dirty_bitmap(bmds->dirty_bitmap, sector, nr_sectors);
>> > > +            sector += nr_sectors;
>> > > +            bmds->cur_dirty = sector;
>> > > +
>> > >              break;
>> > >          }
>> > >          sector += BDRV_SECTORS_PER_DIRTY_CHUNK;
>> > > -- 
>> > > 1.8.3.1
>> > > 
>> > 
>> > Nice catch above all, thank you!
>> > 
>> > Reviewed-by: Fam Zheng <famz@redhat.com>
>> 
>> Are you taking that via a block pull?
>
> I can do that, but I'm not sure whether it should go to 2.9. This is a
> performance improvement, which usually doesn't qualify as bug fixes. But this
> also looks like a mistake in original code.
>
> Fam

I am taking it through migration and push it.  I agree with your description.