Re: CFQ v2 high cpu load fix(?)

Prakash K. Cheemplavam
2004-10-12T20:46:03Z

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Nick Piggin schrieb:
> Jens Axboe wrote:
>
>> On Tue, Oct 12 2004, Nick Piggin wrote:
>>
>>> Ronny V. Vindenes wrote:
>>>
>>>>
>>>> --- patches/linux-2.6.9-rc4-ck1/drivers/block/ll_rw_blk.c
>>>> 2004-10-12 12:25:09.798003278 +0200
>>>> +++ linux-2.6.9-rc4-ck1/drivers/block/ll_rw_blk.c 2004-10-12
>>>> 12:25:42.959479479 +0200
>>>> @@ -100,7 +100,7 @@
>>>> nr = q->nr_requests;
>>>> q->nr_congestion_on = nr;
>>>>
>>>> - nr = q->nr_requests - (q->nr_requests / 8) - 1;
>>>> + nr = q->nr_requests - (q->nr_requests / 8) -
>>>> (q->nr_requests/16)- 1;
>>>> if (nr < 1)
>>>> nr = 1;
>>>> q->nr_congestion_off = nr;
>>>
>>>
>>>
>>> I thought this first hunk looked like a good idea when Arjan sent the
>>> patch. Can you check if it alone helps your problem?
>>
>>
>>
>> Yeah agree, it's a good idea to leave a bit of air between congestion on
>> and off. Fully explains the cfq v2 excessive sys time for some
>> workloads, which is extra nice.
>>
>
> Cool. Can you queue up a patch for when -mm opens again, or shall I?
> I can't imagine it should cause any problems but a bit of testing
> would be wise.

Just as a feedback: I applied the first hunk of that patch to
2.6.9-rc4-ck1 and it really makes a difference. At first I thought the
staircase scheduler was responsible for io starvation sometimes, but now
this behaviour is gone. Very well!

Prakash

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