cfq-iosched: adapt slice to number of processes doing I/O

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When the number of processes performing I/O concurrently increases,
a fixed time slice per process will cause large latencies.

This patch, if low_latency mode is enabled,  will scale the time slice
assigned to each process according to a 300ms target latency.

In order to keep fairness among processes:
* The number of active processes is computed using a special form of
running average, that quickly follows sudden increases (to keep latency low),
and decrease slowly (to have fairness in spite of rapid decreases of this
value).

To safeguard sequential bandwidth, we impose a minimum time slice
(computed using 2*cfq_slice_idle as base, adjusted according to priority
and async-ness).

Signed-off-by: Corrado Zoccolo <czoccolo@gmail.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

...

This commit is contained in:

Corrado Zoccolo 2009-10-26 22:44:04 +01:00 • committed by Jens Axboe

parent 1a1238a7dd

commit 5db5d64277

1 changed files with 51 additions and 2 deletions

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block/cfq-iosched.c

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