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Re: [Xen-devel] about hot plug issue

To: "Yu, Ping Y" <ping.y.yu@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] about hot plug issue
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Tue, 26 Sep 2006 10:15:10 +0100
Cc: sos22@xxxxxxxxx, Steven Hand <steven.hand@xxxxxxxxxxxx>, Christian.Limpach@xxxxxxxxxxxxx
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On 26/9/06 09:26, "Yu, Ping Y" <ping.y.yu@xxxxxxxxx> wrote:

>> How long do the creation commands appear to hang before timing out?
> With the
>> new timeouts it ought to be at least a minute, which ought to be plenty
> of
>> time to create a dozen domains.
> The failure time is about 140 second.

Well, dom0 is probably hosed for those 140 seconds and you've reached the
limit of work that can be done in single-VCPU domain 0 in that amount of
time. Also, a user is not going to want to wait an unbounded length of time
for his request to be processed -- it seems reasonable to time out, but the
error should probably be 'too busy' rather than 'unknown fatal error'. And
the timeout should be more easily user-adjustable (2 minutes is a long time
for a user to stare at an idle console).

Or we could work out how we are chewing up dom0 for 10s per created domain.
Is the total time to create 12 domains less if you create them one after
another (serially) rather than issuing the xm requests all at the same time?
I wonder if creating many domains in parallel is thrashing domain 0 somehow.

>>> At the same time, we found when main_loop_wait is increased to
>>> 100 ms, windows guest's keyboard and mouse response is
>>> significantly slower.
>> Perhaps we need a single polling daemon that can demux kb/mouse events
> to
>> all qemu instances in a way that can be select()ed on. That would avoid
>> unscalable polling overheads.
> Good solution. Could you make a patch for this? :-)

I need to discuss with other Cambridge folks. Moving to qemu stub domain and
split driver for kb/mouse input will solve this issue anyway in the longer

 -- Keir

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