Messages in this thread | | | From | Jeff Moyer <> | Subject | Re: [PATCH 4/4] cfq-iosched: fix corner cases in idling logic | Date | Wed, 02 Dec 2009 09:47:59 -0500 |
| |
Vivek Goyal <vgoyal@redhat.com> writes:
> On Wed, Dec 02, 2009 at 03:14:22PM +0100, Corrado Zoccolo wrote: >> Hi Jeff, >> On Wed, Dec 2, 2009 at 2:42 PM, Jeff Moyer <jmoyer@redhat.com> wrote: >> > Corrado Zoccolo <czoccolo@gmail.com> writes: >> > >> >> Idling logic was disabled in some corner cases, leading to unfair share >> >> for noidle queues. >> >> * the idle timer was not armed if there were other requests in the >> >> driver. unfortunately, those requests could come from other workloads, >> >> or queues for which we don't enable idling. So we will check only >> >> pending requests from the active queue >> >> * rq_noidle check on no-idle queue could disable the end of tree idle if >> >> the last completed request was rq_noidle. Now, we will disable that >> >> idle only if all the queues served in the no-idle tree had rq_noidle >> >> requests. >> >> >> >> Reported-by: Vivek Goyal <vgoyal@redhat.com> >> >> Signed-off-by: Corrado Zoccolo <czoccolo@gmail.com> >> > >> >> @@ -2606,17 +2608,27 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq) >> >> cfq_clear_cfqq_slice_new(cfqq); >> >> } >> >> /* >> >> - * If there are no requests waiting in this queue, and >> >> - * there are other queues ready to issue requests, AND >> >> - * those other queues are issuing requests within our >> >> - * mean seek distance, give them a chance to run instead >> >> - * of idling. >> >> + * Idling is not enabled on: >> >> + * - expired queues >> >> + * - idle-priority queues >> >> + * - async queues >> >> + * - queues with still some requests queued >> >> + * - when there is a close cooperator >> >> */ >> > >> > I'm not sure this logic is correct. Is this for the 2.6.33 branch? >> Yes. >> > If so, the coop flag now means that multiple processes share the same >> > cfqq. Are you sure this is the right thing to do for close cooperators? >> I'm not sure. I didn't change the logic for close cooperators:
Heh, right you are.
>> - else if (cfqq_empty && !cfq_close_cooperator(cfqd, cfqq) && >> - sync && !rq_noidle(rq)) >> - cfq_arm_slice_timer(cfqd); >> + else if (sync && cfqq_empty && >> + !cfq_close_cooperator(cfqd, cfqq)) { >> + cfqd->noidle_tree_requires_idle |= !rq_noidle(rq); >> >> I changed the rq_noidle part, and rewrote the comment to be aligned >> with the code. >> So I don't mind if you improve (or just remove) the close cooperator part. >> Probably, you should do a test where close cooperating processes are competing >> with a sequential reader, to see the effect of idling or not on them. >> > > I also can't find what's wrong with this. Previously we were not merging > close cooperators in a single queue. So if we found a close cooperator > we chose to not idle and move to that close cooperator. Now we try to > merge all the close cooperators in a single queue. But that merging has > not taken place yet and will happen when next request comes.
The coop flag is not set until the merge has taken place.
> A normal sequential reader will not find the close cooperator. Only the > queues which should be merged will find the close cooperator. If anyway > these queues are going to be merged soon, there is proably no point in > continuing to idle on this queue in case we found a close cooperator. > > So, to me even in new code by jeff, it probably is fine to continue with > policy of not idling if we found a close cooperator.
That would mean changing the check from cfqq_coop to cfqq->new_queue != NULL.
Cheers, Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |