Messages in this thread | | | From | Divyesh Shah <> | Date | Fri, 24 Jul 2009 13:49:40 -0700 | Subject | Re: [PATCH] block: Improve think time sampling for CFQ |
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On Wed, Jul 15, 2009 at 2:52 PM, Vivek Goyal<vgoyal@redhat.com> wrote: > On Thu, Jul 16, 2009 at 02:56:54AM +0530, Divyesh Shah wrote: >> Avoid taking a think time sample when the cfqq is not a sync queue or not >> currently active or till its first request in the ongoing timeslice >> completes. >> > > Hi Divyesh, > > It would be nice to give some more details in changelog regarding why are > you donig this change.
Hi Vivek, It seems like I misunderstood the last_end_request and the io_thinktime calculations. Please ignore this patch.
> > >> Signed-off by: Divyesh Shah <dpshah@google.com> >> --- >> This applies to Linus's kernel tree. >> >> block/cfq-iosched.c | 15 +++++++++++---- >> 1 files changed, 11 insertions(+), 4 deletions(-) >> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c >> index fd7080e..1657d4f 100644 >> --- a/block/cfq-iosched.c >> +++ b/block/cfq-iosched.c >> @@ -1904,10 +1904,17 @@ err: >> } >> >> static void >> -cfq_update_io_thinktime(struct cfq_data *cfqd, struct cfq_io_context *cic) >> +cfq_update_io_thinktime(struct cfq_data *cfqd, struct cfq_queue *cfqq, >> + struct cfq_io_context *cic) >> { >> - unsigned long elapsed = jiffies - cic->last_end_request; >> - unsigned long ttime = min(elapsed, 2UL * cfqd->cfq_slice_idle); >> + unsigned long elapsed, ttime; >> + >> + if (!cfq_cfqq_sync(cfqq) || cfqq != cfqd->active_queue || >> + cfq_cfqq_slice_new(cfqq)) >> + return; > > If we take a valid sample only when cfqq is the active queue, I think it > will take a long time before idling is enabled back? > > For example consider a queue for which idling got disabled for some > reason. Now that queue will be scheduled in and after completion of > request, we will not idle and immediately expire the queue. For sequential > readers, next request most likely will come after the expiry of the queue. > Now this queue is not active, so when next request comes in, that sample > will not be valid and we will never enable the idling on this queue? > > I am not sure what are you trying to solve here. I guess that you are > concerned about the case where a reader can drive queue depth more than 1. > So after first request when next request comes in, it is probably not very > fair to compare it with cic->last_end_request. Instead it should be > compared with arrival time of previous request? > > If yes, then we can probably maintain another variable, cic->last_req_arrival > and calculate elapsed time based on last_req_arrival only if it is after > the last_end_request. May be something like as follows. > > if (time_after(cic->last_req_arrival, cic->last_end_request)) > elapsed = jiffies - cic->last_req_arrival; > else > elapsed = jiffies - cic->last_end_request; > > One more question, why are you not considering a sample valid if slice_new > is set for the active queue? I think with introduction of > last_req_arrival, we probably would not need it. > > Thanks > Vivek > >> + >> + elapsed = jiffies - cic->last_end_request; >> + ttime = min(elapsed, 2UL * cfqd->cfq_slice_idle); >> >> cic->ttime_samples = (7*cic->ttime_samples + 256) / 8; >> cic->ttime_total = (7*cic->ttime_total + 256*ttime) / 8; >> @@ -2072,7 +2079,7 @@ cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq, >> if (rq_is_meta(rq)) >> cfqq->meta_pending++; >> >> - cfq_update_io_thinktime(cfqd, cic); >> + cfq_update_io_thinktime(cfqd, cfqq, cic); >> cfq_update_io_seektime(cfqd, cic, rq); >> cfq_update_idle_window(cfqd, cfqq, cic); >> > -- 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/
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