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Date: Sun, 13 Jul 2008 03:11:23 +0200
From: Kris Kennaway <kris@FreeBSD.org>
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To: Nate Eldredge <neldredge@math.ucsd.edu>
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Cc: freebsd-hackers@freebsd.org
Subject: Re: SCHED_4BSD bad interactivity on 7.0 vs 6.3
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Nate Eldredge wrote:
> Hi folks,
> 
> Hopefully this is a good list for this topic.
> 
> It seems like there has been a regression in interactivity from 
> 6.3-RELEASE to 7.0-RELEASE when using the SCHED_4BSD scheduler.  After 
> upgrading my single-cpu amd64 box, 7.0 has much worse latency.  When 
> running a kernel compile, there is a noticeable lag to echo my typing or 
> scroll my browser windows, and playing an mp3 frequently cuts out for a 
> second or two.  This did not happen on 6.3-RELEASE.

Are you sure it's not the x.org server bug that was present in the 
version shipped with 7.0?  Update to the latest version and see if your 
X interactivity improves.

Kris

> I wrote a small program which forks two processes that run 
> gettimeofday() in a tight loop to see how long they get scheduled out.  
> On 6.3 the maximum latency is usually under 100 ms.  On 7.0 it is 500 ms 
> or more even when nothing else is running on the system.  When a compile 
> is also running it is sometimes 1400 ms or more.
> 
> SCHED_ULE is much better, so I've switched over.  But it's not the 
> default yet, and most people are still going to be using SCHED_4BSD.  It 
> used to be acceptable but now it isn't.  Does anyone know why it's 
> regressed so badly?
>