Il giorno 22/apr/2016, alle ore 20:41, Tejun Heo <[email protected]> ha scritto:
> 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. >> >> It’s the same. But this is the part I’m 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? > That’s exactly the source of my confusion: why does the worker walk through different cgroups all the time if the I/O is originated by the same process, which never changes group? Thanks, Paolo > Thanks. > > -- > tejun
