lkml.org 
[lkml]   [2019]   [Jun]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 4/9] blkcg: implement REQ_CGROUP_PUNT
On Sat 15-06-19 11:24:48, Tejun Heo wrote:
> When a shared kthread needs to issue a bio for a cgroup, doing so
> synchronously can lead to priority inversions as the kthread can be
> trapped waiting for that cgroup. This patch implements
> REQ_CGROUP_PUNT flag which makes submit_bio() punt the actual issuing
> to a dedicated per-blkcg work item to avoid such priority inversions.
>
> This will be used to fix priority inversions in btrfs compression and
> should be generally useful as we grow filesystem support for
> comprehensive IO control.
>
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Reviewed-by: Josef Bacik <josef@toxicpanda.com>
> Cc: Chris Mason <clm@fb.com>

...

> +bool __blkcg_punt_bio_submit(struct bio *bio)
> +{
> + struct blkcg_gq *blkg = bio->bi_blkg;
> +
> + /* consume the flag first */
> + bio->bi_opf &= ~REQ_CGROUP_PUNT;
> +
> + /* never bounce for the root cgroup */
> + if (!blkg->parent)
> + return false;
> +
> + spin_lock_bh(&blkg->async_bio_lock);
> + bio_list_add(&blkg->async_bios, bio);
> + spin_unlock_bh(&blkg->async_bio_lock);
> +
> + queue_work(blkcg_punt_bio_wq, &blkg->async_bio_work);
> + return true;
> +}
> +

So does this mean that if there is some inode with lots of dirty data for a
blkcg that is heavily throttled, that blkcg can occupy a ton of workers all
being throttled in submit_bio()? Or what is constraining a number of
workers one blkcg can consume?

Honza

--
Jan Kara <jack@suse.com>
SUSE Labs, CR

\
 
 \ /
  Last update: 2019-06-20 17:39    [W:0.131 / U:70.332 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site