Re: Linux disk performance.

[Arjan van de Ven]

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 didnÂt 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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