Message-ID: <44770A12.9010904@bigpond.net.au>
Date: Sat, 27 May 2006 00:00:50 +1000
From: Peter Williams <pwil3058@bigpond.net.au>
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To: Con Kolivas <kernel@kolivas.org>
CC: Mike Galbraith <efault@gmx.de>,
       Linux Kernel <linux-kernel@vger.kernel.org>,
       Kingsley Cheung <kingsley@aurema.com>, Ingo Molnar <mingo@elte.hu>,
       Rene Herman <rene.herman@keyaccess.nl>
Subject: Re: [RFC 0/5] sched: Add CPU rate caps
References: <20060526042021.2886.4957.sendpatchset@heathwren.pw.nest> <200605262109.20808.kernel@kolivas.org>
In-Reply-To: <200605262109.20808.kernel@kolivas.org>
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Con Kolivas wrote:
> On Friday 26 May 2006 14:20, Peter Williams wrote:
>> These patches implement CPU usage rate limits for tasks.
>>
>> Although the rlimit mechanism already has a CPU usage limit (RLIMIT_CPU)
>> it is a total usage limit and therefore (to my mind) not very useful.
>> These patches provide an alternative whereby the (recent) average CPU
>> usage rate of a task can be limited to a (per task) specified proportion
>> of a single CPU's capacity.  The limits are specified in parts per
>> thousand and come in two varieties -- hard and soft.  The difference
>> between the two is that the system tries to enforce hard caps regardless
>> of the other demand for CPU resources but allows soft caps to be
>> exceeded if there are spare CPU resources available.  By default, tasks
>> will have both caps set to 1000 (i.e. no limit) but newly forked tasks
>> will inherit any caps that have been imposed on their parent from the
>> parent.  The mimimim soft cap allowed is 0 (which effectively puts the
>> task in the background) and the minimim hard cap allowed is 1.
>>
>> Care has been taken to minimize the overhead inflicted on tasks that
>> have no caps and my tests using kernbench indicate that it is hidden in
>> the noise.
> 
> The presence of tasks with caps will break smp balancing and smp nice. I 
> suspect you could probably provide a reasonable workaround by altering their 
> priority bias effect in the raw weighted load in smp nice for soft caps by 
> the percentage cpu of the cap. Hard caps provide more "interesting" 
> challenges though. I can't think of a valid biasing off hand for them, but at 
> least initially using the same logic as soft caps should help.
> 

I thought that I already did that?  Check the changes to set_load_weight().

-- 
Peter Williams                                   pwil3058@bigpond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
  -- Ambrose Bierce
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