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

[Kevin Wolf <kwolf@redhat.com>]

Am 15.03.2017 um 04:37 hat Lidong Chen geschrieben:
> 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;

sector += BDRV_SECTORS_PER_DIRTY_CHUNK would be acceptable here...

> +            bmds->cur_dirty = sector;
> +
>              break;
>          }
>          sector += BDRV_SECTORS_PER_DIRTY_CHUNK;
>          bmds->cur_dirty = sector;
>      }

...which would make it the same code as the rest of the loop. It could
be nicer to reuse the same code and just set a bool when a request is
submitted so that the loop terminates after that.

But that's just a matter of taste, so I'll still give:

Reviewed-by: Kevin Wolf <kwolf@redhat.com>