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Re: [Xen-devel] unnecessary VCPU migration happens again

To: "Xu, Anthony" <anthony.xu@xxxxxxxxx>
Subject: Re: [Xen-devel] unnecessary VCPU migration happens again
From: Emmanuel Ackaouy <ack@xxxxxxxxxxxxx>
Date: Thu, 21 Dec 2006 17:22:46 +0100
Cc: "Petersson, Mats" <Mats.Petersson@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, xen-ia64-devel <xen-ia64-devel@xxxxxxxxxxxxxxxxxxx>
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Hi Anthony.

Based on the number of "ticks" on CPU0 that occurred between the
two stat dumps, over 16 minutes elapsed during that time.

During that time, 364 regular migrations occurred. These are migrations
that happen when an idle CPU finds a runnable VCPU queued elsewhere
on the system.

Also during that time, 530 multi-core load balancing migrations happened.

That's about one such migration every 1.86 seconds. I'm somewhat surprised that this costs 5% in performance of your benchmark. That said, the point of this code is to balance a partially idle system and not to shuffle things around too much so I'm happy to smooth the algorithm further to reduce the
number of these migrations.

I'll send another patch shortly.

On Dec 20, 2006, at 4:26, Xu, Anthony wrote:
Before running KB

(XEN)   migrate_queued                 = 169
(XEN)   migrate_running                = 213

(XEN) CPU[00]  tick=117181, sort=12233, sibling=0x1, core=0x5

After running KB

(XEN)   migrate_queued                 = 533
(XEN)   migrate_running                = 743

(XEN) CPU[00]  tick=215790, sort=42999, sibling=0x1, core=0x5

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