Re: [RFC,PATCH] cfq-iosched: improve async queue ramp up formula

[Jens Axboe <jens.axboe@oracle.com>]

On Thu, Nov 26 2009, Corrado Zoccolo wrote:
> The introduction of ramp-up formula for async queue depths has
> slowed down dirty page reclaim, by reducing async write performance.
> This patch improves the formula by considering the remaining slice.
> 
> The new formula will allow more dispatches at the beginning of the
> slice, reducing them at the end.
> This will ensure that we achieve good throughput, without the risk of
> overrunning the allotted timeslice.
> 
> The threshold is automatically increased when sync I/O is not
> intermingled with async, in accordance with the previous incarnation of
> the formula.

The slow ramp up is pretty much essential to being able to have low
latency for the sync reads, so I'm afraid this will break that. I would
prefer doing it through memory reclaim detection, like the other patch
you and Motohiro suggested.

-- 
Jens Axboe