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Date: Wed, 28 Mar 2012 17:32:28 -0700 From: Greg KH <gregkh@...uxfoundation.org> To: Tao Ma <tm@....ma> Cc: linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk> Subject: Re: [PATCH] block: Make cfq_target_latency tunable through sysfs. On Tue, Mar 27, 2012 at 04:16:53PM +0800, Tao Ma wrote: > From: Tao Ma <boyu.mt@...bao.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. If you add/modify sysfs files, you HAVE to also have a matching change to Documentation/ABI. Please do so. thanks, greg k-h -- 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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