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Date: Wed, 30 Mar 2011 20:59:34 -0700 From: Justin TerAvest <teravest@...gle.com> To: Vivek Goyal <vgoyal@...hat.com> Cc: Jens Axboe <jaxboe@...ionio.com>, lkml <linux-kernel@...r.kernel.org>, Chad Talbott <ctalbott@...gle.com> Subject: Re: Why do we use cpu nice priority for ioprio? On Wed, Mar 30, 2011 at 11:34 AM, Vivek Goyal <vgoyal@...hat.com> wrote: > On Wed, Mar 30, 2011 at 11:23:45AM -0700, Justin TerAvest wrote: >> On Fri, Mar 25, 2011 at 12:48 AM, Jens Axboe <jaxboe@...ionio.com> wrote: >> > On 2011-03-25 03:38, Justin TerAvest wrote: >> >> It's not clear why the cpu nice value should be mapped to the ioprio >> >> for a task when none is picked. >> >> >> >> Internally, at cfq_init_prio_data(), we just set: >> >> ioprio = IOPRIO_NORM; >> >> ioprio_class = IOPRIO_CLASS_BE; >> >> if ioprio_class is IOPRIO_CLASS_NONE. >> >> >> >> >> >> The problem is that today, SCHED_RR and SCHED_FIFO threads >> >> automatically get bumped up to RT class. This all happens behind the >> >> curtains and the io_class of the thread is still shown as NONE with >> >> sys_ioprio_get(). What's the motivation behind this promotion of >> >> ioprio class? >> > >> > It was decided back in the day when io priorities were introduced. I >> > still think it's a good idea. >> >> This is the part I'm especially curious about. If we're managing the >> resources separately, >> why should be be adjusting io_class based on the nice value? > > What's wrong with taking a hint about ioclass and ioprio from cpu > scheduling class and nice value? I guess it's fine. I was just curious how strongly everyone felt about the way it works today. It sounds like we expect nice values and io scheduling classes to be closely matched. Thanks, Justin > > I think in general if some task is important from cpu perspective then > most likely it is important from IO perspective too. And if user thinks > otherwise, then one can explicitly set ioclass and ioprio of the task. > > So this makes sense to me. > > Thanks > Vivek > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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