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Date: Fri, 27 Nov 2009 09:42:39 +0800 From: Gui Jianfeng <guijianfeng@...fujitsu.com> To: Corrado Zoccolo <czoccolo@...il.com> CC: Jens Axboe <jens.axboe@...cle.com>, Vivek Goyal <vgoyal@...hat.com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH] cfq: Make use of service count to estimate the rb_key offset Corrado Zoccolo wrote: > Hi Gui, Jens > On Thu, Nov 26, 2009 at 7:20 AM, Gui Jianfeng > <guijianfeng@...fujitsu.com> wrote: >> Hi Jens, Czoccolo >> >> For the moment, different workload cfq queues are put into different >> service trees. But CFQ still uses "busy_queues" to estimate rb_key >> offset when inserting a cfq queue into a service tree. I think this >> isn't appropriate, and it should make use of service tree count to do >> this estimation. This patch is for for-2.6.33 branch. > > In cfq_choose_wl, we rely on consistency of rb_keys across service > trees to compute the next workload to be serviced. > for (i = 0; i < 3; ++i) { > /* otherwise, select the one with lowest rb_key */ > queue = cfq_rb_first(service_tree_for(prio, i, cfqd)); > if (queue && > (!key_valid || time_before(queue->rb_key, lowest_key))) { > lowest_key = queue->rb_key; > cur_best = i; > key_valid = true; > } > } > > If you change how the rb_key is computed (so it is no longer > consistent across service trees) without changing how it is used can > introduce problems. Ok, I think I was missing this part. This part still behaves like old CFQ regardless of workload type. I'm wondering why you prefer starting from sync no-idle only when priorities switched, after that, you do it like old CFQ behavior? In order to improve latency for sync no-idle workload, is it possible to take workload type into account, not only rely on rb_keys across service trees? Thanks, Gui > > Thanks, > Corrado > >> Signed-off-by: Gui Jianfeng <guijianfeng@...fujitsu.com> >> --- >> block/cfq-iosched.c | 8 ++++++-- >> 1 files changed, 6 insertions(+), 2 deletions(-) >> >> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c >> index 1bcbd8c..467981e 100644 >> --- a/block/cfq-iosched.c >> +++ b/block/cfq-iosched.c >> @@ -600,11 +600,15 @@ cfq_find_next_rq(struct cfq_data *cfqd, struct cfq_queue *cfqq, >> static unsigned long cfq_slice_offset(struct cfq_data *cfqd, >> struct cfq_queue *cfqq) >> { >> + struct cfq_rb_root *service_tree; >> + >> + service_tree = service_tree_for(cfqq_prio(cfqq), cfqq_type(cfqq), cfqd); >> + >> /* >> * just an approximation, should be ok. >> */ >> - return (cfqd->busy_queues - 1) * (cfq_prio_slice(cfqd, 1, 0) - >> - cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio)); >> + return service_tree->count * (cfq_prio_slice(cfqd, 1, 0) - >> + cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio)); >> } >> >> /* >> -- >> 1.5.4.rc3 >> >> -- >> Regards >> Gui Jianfeng >> >> > > > -- 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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