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Re: [Xen-devel] credit based scheduler

  • To: "Emmanuel Ackaouy" <ack@xxxxxxxxxxxxx>
  • From: "Molle Bestefich" <molle.bestefich@xxxxxxxxx>
  • Date: Thu, 22 Jun 2006 12:26:02 +0200
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Thu, 22 Jun 2006 03:26:23 -0700
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  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>

Emmanuel Ackaouy wrote:
Let me know if you have any other questions.
It's useful to discuss design philosophy on the list.

Well, if you don't mind! :-)...

The first sentence was actually a question too:
Migrating 1 VCPU across 2 CPUs, or
swapping all 3 VCPUs around in a ring-fashion?

To explain myself a bit more, I was wondering whether the scheduler
conceptually can be said to work a little like this (VCPUs mapped to
CPUs in a "ring-fashion"):

(VCPUs = A, B, C)

Time     CPU1  CPU2
0ms      A     B
30ms     B     C
60ms     C     A
90ms     A     B
120ms    B     C

This would give 30ms slices with a time-to-wait for scheduling of 30ms.

Or perhaps more like this:
Time     CPU1  CPU2
0ms      A     B
30ms     A     C
60ms     B     C
90ms     B     A
120ms    C     A

Which gives 60ms slices (warmer cache, yummi) but still with a
time-to-wait for scheduling of 30ms.

The latter obviously being a better algorithm, cache-wise...

Hope it's not stupid questions :-).

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