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Re: [Xen-devel] Why is the credit scheduler better than SEDF

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Subject: Re: [Xen-devel] Why is the credit scheduler better than SEDF
From: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
Date: Wed, 21 Mar 2007 04:19:57 +0000
Cc: Ming Chang <mingchieh.xen@xxxxxxxxx>
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> I read Xen interface manual, and see the following part in the section 2.5
> "SEDF will be going away and its use should be avoided once the credit
> scheduler has stabilized and become the default"
> I think it means SEDF is a temporary scheduler and credit scheduler is
> better
> I want to understand why the credit scheduling is better? And Is there any
> problem with SEDF?

I think SEDF had some bugs / some unfortunate behaviours on some workloads, 
but I don't know the details offhand.  There may be some explanations in the 
mailing list archives.

> and, so far as I know, EDF does not work well in the SMP how about SEDF and
> credit scheuler?

One of the nice advances of the credit scheduler is that it implements work 
stealing so that an idle CPU will be able to take VCPUs off the scheduler 
queues of other processors.  This helps make sure the hardware utilisation is 
good and avoids the user having to do pinning and load balancing manually 
from userspace (although it does support fairly flexible policy regarding 
what PCPUs a VCPU can run on - this is also an advance on SEDF).


Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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