Re: [PATCH] O13int for interactivity

From: Nick Piggin <piggin@cyberone.com.au>
To: Con Kolivas <kernel@kolivas.org>
Cc: linux kernel mailing list <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@osdl.org>, Ingo Molnar <mingo@elte.hu>,
	Felipe Alfaro Solana <felipe_alfaro@linuxmail.org>
Subject: Re: [PATCH] O13int for interactivity
Date: Tue, 05 Aug 2003 12:21:19 +1000	[thread overview]
Message-ID: <3F2F149F.1020201@cyberone.com.au> (raw)
In-Reply-To: <200308051220.04779.kernel@kolivas.org>

Con Kolivas wrote:

>On Tue, 5 Aug 2003 12:11, Nick Piggin wrote:
>
>>Con Kolivas wrote:
>>
>>>Changes:
>>>
>>>Reverted the child penalty to 95 as new changes help this from hurting
>>>
>>>Changed the logic behind loss of interactive credits to those that burn
>>>off all their sleep_avg
>>>
>>>Now all tasks get proportionately more sleep as their relative bonus drops
>>>off. This has the effect of detecting a change from a cpu burner to an
>>>interactive task more rapidly as in O10.
>>>
>>>The _major_ change in this patch is that tasks on uninterruptible sleep do
>>>not earn any sleep avg during that sleep; it is not voluntary sleep so
>>>they should not get it. This has the effect of stopping cpu hogs from
>>>gaining dynamic priority during periods of heavy I/O. Very good for the
>>>jerks you may see in X or audio skips when you start a whole swag of disk
>>>intensive cpu hogs (eg make -j large number). I've simply dropped all
>>>their sleep_avg, but weighting it may be more appropriate. This has the
>>>side effect that pure disk tasks (eg cp) have relatively low priority
>>>which is why weighting may be better. We shall see.
>>>
>>I don't think this is a good idea. Uninterruptible does not mean its
>>not a voluntary sleep. Its more to do with how a syscall is implemented.
>>I don't think it should be treated any differently to any other type of
>>sleep.
>>
>>Any task which calls schedule in kernel context is sleeping volintarily
>>- if implicity due to having called a blocking syscall.
>>
>>
>>>Please test this one extensively. It should _not_ affect I/O throughput
>>>per se, but I'd like to see some of the I/O benchmarks on this. I do not
>>>want to have detrimental effects elsewhere.
>>>
>>Well the reason it can affect IO thoughput is for example when there is
>>an IO bound process and a CPU hog on the same processor: the longer the
>>IO process has to wait (after being woken) before being run, the more
>>chance the disk will fall idle for a longer period. And of course the
>>CPU uncontended case is somewhat uninteresting when it comes to a CPU
>>scheduler.
>>
>
>I've already posted a better solution in O13.1
>
>

No, this still special-cases the uninterruptible sleep. Why is this
needed? What is being worked around? There is probably a way to
attack the cause of the problem.