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[Xen-devel] Questions about Domain switching overhead for Xen 3.0

To: "Ryan Harper" <ryanh@xxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] Questions about Domain switching overhead for Xen 3.0
From: "Amitayu Das" <amitayudas@xxxxxxxxx>
Date: Wed, 3 May 2006 19:27:24 -0400
Delivery-date: Wed, 03 May 2006 16:27:44 -0700
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Can I ask you few quick questions about sedf scheduler available with Xen 3.0?

1. Say, there are two domains apart from Dom0, each with default setting for slice/period length (which is (0,100) with extra flag on). Dom0 is running with default setting for slice/period length of (15,20). Now, is it the fact that irrespective of the loads experienced due to applications running inside the domains, a domain switching happens every 0.5 ms? We measured (hopefully correctly) that the context-switch (or domain-switch, to be precise) overhead is around 10 microsec. If the answer is yes, then would this mean that Xen spends 1% of its time every 0.5 ms just for switching domains? Is that a tolerable limit if efficiency is considered? Please let me know.

2. Why is the default setting for Dom0 is (15, 20) and why the default period length (coded in sched_sedf.c, if I'm not wrong) is 100 ms? Are there any justifications for these values which has not been documented?

Thanks in advance,

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