Re: [PATCH RFC 10/22] block, bfq: add full hierarchical scheduling and cgroups support
From: Tejun Heo
Date: Fri Apr 22 2016 - 14:41:17 EST
Hello, Paolo.
On Fri, Apr 22, 2016 at 08:19:47PM +0200, Paolo Valente wrote:
> > So, a kworker would jump through different workqueues and issue IOs
> > for different writeback domains and the context can't be tied to the
> > issuing task. The cgroup membership should be determined directly
> > from the bio.
>
> Yes. My doubt arises from the fact that the only source of intense I/O
> is the dd (I have executed it alone). In contrast, group changes occur
> at a high frequency during all the execution of the dd. Apparently I
> cannot see any other I/O induced by the dd. Journaling issues sync
> requests.
>
> > cfq uses per-cgroup async queue. I'm not sure how this
> > would map to bfq tho.
>
> Itâs the same. But this is the part Iâm checking.
Ah, right, I was confused. cic is always associated with the task and
yes a writeback worker can trigger blkcg changed events frequently as
it walks through different cgroups. Is this an issue?
Thanks.
--
tejun