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Date: Fri, 02 Sep 2011 14:40:43 -0600 From: Jens Axboe <axboe@...nel.dk> To: Maxim Patlasov <maxim.patlasov@...il.com> CC: linux-kernel@...r.kernel.org Subject: Re: [PATCH v2] cfq: queued/in_driver stats On 2011-09-02 11:02, Maxim Patlasov wrote: > The patch implements gathering and exporting statistics for cfqd->rq_queued > and cfqd->rq_in_driver. Average values of queued/in_driver are visible via > /sys/.../iosched/queued_avg and /sys/.../iosched/in_driver_avg correspondingly. > The output is in form of "%lu.%02lu %lu.%02lu %lu.%02lu" where the first > value represents average over 1 sec interval, the second - over 5 sec, > the third - over 15 sec. > > The patch also exports cfqd->hw_tag to be seen via /sys/.../iosched/hw_tag. > > Seeing hw_tag is useful to be sure that cfq detected NCQ correctly on given > h/w. queued/in_driver stats are useful to debug performance problems: e.g., > if you know that fast h/w raid is able to concurrently process many requests > quite effectively, but at the same time you observe high queued average and > low in_driver one, you can suggest that cfq underloads h/w raid. > > Changes since first version: do_div was used wrongly, fixed. Seems like an awful lot of code for something that could be gleaned with blktrace? -- Jens Axboe -- 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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