Messages in this thread | | | Date | Tue, 23 Aug 2011 12:56:02 +0400 | Subject | Re: [PATCH 1/1] CFQ: fix handling 'deep' cfqq | From | Maxim Patlasov <> |
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Hi,
>> An aproach suggested here avoids performance degradations mentioned above. >> With this patch applied, the performance on slow hdd is the same as it used >> to be before 8e1ac6655104bc6e1e79d67e2df88cc8fa9b6e07, and, on fast h/w-raids, >> it's roughly the same as for noop scheduler or CFQ with slice_idle=0. > idle is a usual cause of cfq performance issue. did you have test in > disk without NCQ?
Yes, on the node with "slow hdd" CFQ detected it as hw_tag=0. I explained what I tested in cover message (subj: [PATCH 0/1] CFQ: fixing performance issues).
> And did you test if this will hurt the performance of Vivek's original problem?
No. What's Vivek's original problem?
> snip >> + if (cfq_cfqq_deep_early(cfqq) && cfqq->n_dispatched >= CFQQ_DEEP_THR) { >> + if (cfqq->first_dispatch == jiffies) >> + cfqd->cfq_disk_looks_fast++; >> + else >> + cfqd->cfq_disk_looks_slow++; >> + > jiffies is too coarse here. A disk with NCQ can dispatch several > requests within one jiffy.
If a disk with NCQ dispatches four requests in raw within one jiffy regularly, the patch I suggested will claim it as "fast enough". It should be beneficial to disable idling for deep&seeky cfqq in this case, imho. Anyway, existing code:
> /* > * This is a deep seek queue, but the device is much faster than > * the queue can deliver, don't idle > **/ > if (CFQQ_SEEKY(cfqq) && cfq_cfqq_idle_window(cfqq) && > (cfq_cfqq_slice_new(cfqq) || > (cfqq->slice_end - jiffies > jiffies - cfqq->slice_start))) { > cfq_clear_cfqq_deep(cfqq); > cfq_clear_cfqq_idle_window(cfqq); > } >
would surely disable idling in this case. So, the patch I suggested doesn't make things worse (as compared with existing implementation).
Thanks, Maxim -- 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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