2021-03-05 18:37:15

by Jens Axboe

Subject: Re: [PATCH] blk-cgroup: Fix the recursive blkg rwstat

On 3/5/21 1:13 AM, Xunlei Pang wrote:
> The current blkio.throttle.io_service_bytes_recursive doesn't
> work correctly.
>
> As an example, for the following blkcg hierarchy:
> (Made 1GB READ in test1, 512MB READ in test2)
> test
> / \
> test1 test2
>
> $ head -n 1 test/test1/blkio.throttle.io_service_bytes_recursive
> 8:0 Read 1073684480
> $ head -n 1 test/test2/blkio.throttle.io_service_bytes_recursive
> 8:0 Read 537448448
> $ head -n 1 test/blkio.throttle.io_service_bytes_recursive
> 8:0 Read 537448448
>
> Clearly, above data of "test" reflects "test2" not "test1"+"test2".
>
> Do the correct summary in blkg_rwstat_recursive_sum().

LGTM, Tejun?

>
> Signed-off-by: Xunlei Pang <[email protected]>
> ---
> block/blk-cgroup-rwstat.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/block/blk-cgroup-rwstat.c b/block/blk-cgroup-rwstat.c
> index 85d5790..3304e84 100644
> --- a/block/blk-cgroup-rwstat.c
> +++ b/block/blk-cgroup-rwstat.c
> @@ -109,6 +109,7 @@ void blkg_rwstat_recursive_sum(struct blkcg_gq *blkg, struct blkcg_policy *pol,
>
> lockdep_assert_held(&blkg->q->queue_lock);
>
> + memset(sum, 0, sizeof(*sum));
> rcu_read_lock();
> blkg_for_each_descendant_pre(pos_blkg, pos_css, blkg) {
> struct blkg_rwstat *rwstat;
> @@ -122,7 +123,7 @@ void blkg_rwstat_recursive_sum(struct blkcg_gq *blkg, struct blkcg_policy *pol,
> rwstat = (void *)pos_blkg + off;
>
> for (i = 0; i < BLKG_RWSTAT_NR; i++)
> - sum->cnt[i] = blkg_rwstat_read_counter(rwstat, i);
> + sum->cnt[i] += blkg_rwstat_read_counter(rwstat, i);
> }
> rcu_read_unlock();
> }
>


--
Jens Axboe

2021-03-07 15:07:59

by Tejun Heo

Subject: Re: [PATCH] blk-cgroup: Fix the recursive blkg rwstat

On Fri, Mar 05, 2021 at 11:32:05AM -0700, Jens Axboe wrote:
> On 3/5/21 1:13 AM, Xunlei Pang wrote:
> > The current blkio.throttle.io_service_bytes_recursive doesn't
> > work correctly.
> >
> > As an example, for the following blkcg hierarchy:
> > (Made 1GB READ in test1, 512MB READ in test2)
> > test
> > / \
> > test1 test2
> >
> > $ head -n 1 test/test1/blkio.throttle.io_service_bytes_recursive
> > 8:0 Read 1073684480
> > $ head -n 1 test/test2/blkio.throttle.io_service_bytes_recursive
> > 8:0 Read 537448448
> > $ head -n 1 test/blkio.throttle.io_service_bytes_recursive
> > 8:0 Read 537448448
> >
> > Clearly, above data of "test" reflects "test2" not "test1"+"test2".
> >
> > Do the correct summary in blkg_rwstat_recursive_sum().
>
> LGTM, Tejun?

Gees, that's horrible. Thanks for fixing this.

Acked-by: Tejun Heo <[email protected]>

--
tejun