Messages in this thread | | | Date | Tue, 11 Jan 2011 22:07:47 +0100 | Subject | Re: [PATCH 1/2]block cfq: make queue preempt work for queues from different workload | From | Corrado Zoccolo <> |
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Hi Shaohua, On Tue, Jan 11, 2011 at 9:51 AM, Shaohua Li <shaohua.li@intel.com> wrote: > I got this: > fio-874 [007] 2157.724514: 8,32 m N cfq874 preempt > fio-874 [007] 2157.724519: 8,32 m N cfq830 slice expired t=1 > fio-874 [007] 2157.724520: 8,32 m N cfq830 sl_used=1 disp=0 charge=1 iops=0 sect=0 > fio-874 [007] 2157.724521: 8,32 m N cfq830 set_active wl_prio:0 wl_type:0 > fio-874 [007] 2157.724522: 8,32 m N cfq830 Not idling. st->count:1 > cfq830 is an async queue, and preempted by a sync queue cfq874. But since we > have cfqg->saved_workload_slice mechanism, the preempt is a nop. > Looks currently our preempt is totally broken if the two queues are not from > the same workload type. > Below patch fixes it. This will might make async queue starvation, but it's > what our old code does before cgroup is added. have you measured latency improvements by un-breaking preemption? AFAIK, preemption behaviour changed since 2.6.33, before cgroups were added, and the latency before the changes that weakened preemption in 2.6.33 was far worse.
Thanks, Corrado > > Signed-off-by: Shaohua Li <shaohua.li@intel.com> > > --- > block/cfq-iosched.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > Index: linux/block/cfq-iosched.c > =================================================================== > --- linux.orig/block/cfq-iosched.c 2011-01-11 16:24:56.000000000 +0800 > +++ linux/block/cfq-iosched.c 2011-01-11 16:41:49.000000000 +0800 > @@ -3284,10 +3284,19 @@ cfq_should_preempt(struct cfq_data *cfqd > */ > static void cfq_preempt_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq) > { > + struct cfq_queue *old_cfqq = cfqd->active_queue; > + > cfq_log_cfqq(cfqd, cfqq, "preempt"); > cfq_slice_expired(cfqd, 1); > > /* > + * workload type is changed, don't save slice, otherwise preempt > + * doesn't happen > + */ > + if (cfqq_type(old_cfqq) != cfqq_type(cfqq)) > + cfqq->cfqg->saved_workload_slice = 0; > + > + /* > * Put the new queue at the front of the of the current list, > * so we know that it will be selected next. > */ > > > -- 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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