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

["Amitayu Das" <amitayudas@xxxxxxxxx>]

Hi,

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,
Amitayu

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