Reviewed-by: Zhi Yong Wu <wu...@linux.vnet.ibm.com>
On Wed, 2013-03-20 at 10:12 +0100, Benoît Canet wrote:
> This patch fix an I/O throttling behavior triggered by limiting at 150 iops
> and running a load of 50 threads doing random pwrites on a raw virtio device.
>
> After a few moments the iops count start to oscillate steadily between 0 and a
> value upper than the limit.
>
> As the load keep running the period and the amplitude of the oscillation
> increase until io bursts reaching the physical storage max iops count are
> done.
>
> These bursts are followed by guest io starvation.
>
> As the period of this oscillation cycle is increasing the cause must be a
> computation error leading to increase slowly the wait time.
>
> This patch make the wait time a bit smaller and tests confirm that it solves
> the oscillating behavior.
>
> Signed-off-by: Benoit Canet <ben...@irqsave.net>
> ---
> block.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/block.c b/block.c
> index 0a062c9..455d8b0 100644
> --- a/block.c
> +++ b/block.c
> @@ -3739,7 +3739,7 @@ static bool bdrv_exceed_iops_limits(BlockDriverState
> *bs, bool is_write,
> }
>
> /* Calc approx time to dispatch */
> - wait_time = (ios_base + 1) / iops_limit;
> + wait_time = ios_base / iops_limit;
> if (wait_time > elapsed_time) {
> wait_time = wait_time - elapsed_time;
> } else {
--
Regards,
Zhi Yong Wu
