linux-kernel - Re: BFS vs. mainline scheduler benchmarks and measurements

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Message-ID: <20090907184640.GG18599@kernel.dk>
Date:	Mon, 7 Sep 2009 20:46:40 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Con Kolivas <kernel@...ivas.org>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>
Subject: Re: BFS vs. mainline scheduler benchmarks and measurements

On Mon, Sep 07 2009, Avi Kivity wrote:
> On 09/07/2009 12:49 PM, Jens Axboe wrote:
>>
>> I ran a simple test as well, since I was curious to see how it performed
>> wrt interactiveness. One of my pet peeves with the current scheduler is
>> that I have to nice compile jobs, or my X experience is just awful while
>> the compile is running.
>>    
>
> I think the problem is that CFS is optimizing for the wrong thing.  It's  
> trying to be fair to tasks, but these are meaningless building blocks of  
> jobs, which is what the user sees and measures.  Your make -j128  
> dominates your interactive task by two orders of magnitude.  If the  
> scheduler attempts to bridge this gap using heuristics, it will fail  
> badly when it misdetects since it will starve the really important  
> 100-thread job for a task that was misdetected as interactive.

Agree, I was actually looking into doing joint latency for X number of
tasks for the test app. I'll try and do that and see if we can detect
something from that.

-- 
Jens Axboe

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