Messages in this thread | | | Date | Sun, 01 Apr 2012 14:33:55 -0700 | From | Jens Axboe <> | Subject | Re: [PATCH V2 1/2] block: Make cfq_target_latency tunable through sysfs. |
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On 2012-03-31 08:31, Tao Ma wrote: > From: Tao Ma <boyu.mt@taobao.com> > > In cfq, when we calculate a time slice for a process(or a cfqq to > be precise), we have to consider the cfq_target_latency so that all the > sync request have an estimated latency(300ms) and it is controlled by > cfq_target_latency. But in some hadoop test, we have found that if > there are many processes doing sequential read(24 for example), the > throughput is bad because every process can only work for about 25ms > and the cfqq is switched. That leads to a higher disk seek. We can > achive the good throughput by setting low_latency=0, but then some > read's latency is too much for the application. > > So this patch makes cfq_target_latency tunable through sysfs so that > we can tune it and find some magic number which is not bad for both > the throughput and the read latency.
Thanks, applied both.
-- Jens Axboe
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