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

[Fam Zheng]

On Wed, 03/15 17:31, Dr. David Alan Gilbert wrote:
> * Fam Zheng (address@hidden) 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 <address@hidden>
> > > ---
> > >  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 <address@hidden>
> 
> 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