Messages in this thread | | | Subject | Re: Linux disk performance. | From | Arjan van de Ven <> | Date | Tue, 19 Dec 2006 13:18:06 +0100 |
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On Tue, 2006-12-19 at 17:38 +1100, Nick Piggin wrote: > Manish Regmi wrote: > > > Nick Piggin: > > > >> but > >> they look like they might be a (HZ quantised) delay coming from > >> block layer plugging. > > > > > > Sorry i didn´t understand what you mean. > > When you submit a request to an empty block device queue, it can > get "plugged" for a number of timer ticks before any IO is actually > started. This is done for efficiency reasons and is independent of > the IO scheduler used.
however the O_DIRECT codepath unplugs the queues always immediately..
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