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SubjectRe: [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



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