[Xen-devel] Re: [XENOPROFILE] and "xm vcpu-pin" doesn't work as expected

["Ray Bryant" <raybry@xxxxxxxxxxxxxxxxx>]

Renato,

I've been trying to profile an HVM guest and its corresponding Xen usage so I 
used the "xm vcpu-pin" command to pin the HVM guest to CPU 1 and dom0 to CPU 
0 (this is a single socket, dual core setup, but that probably doesn't matter 
here).

I then used the opsetup --separate=cpu option to split out the profile samples 
by CPU, fully expecting to see no "domain1-xen" samples on CPU 0.   However, 
what I actually see is 90% (more or less) of the samples on CPU 0 and the 
remainder on CPU 1.

This problem occurs on both AMD V and VT.

So, I guess the question is:

(1)   Is xenoprof reporting the correct CPU, or
(2)   Does "xm vcpu-pin" really do what it claims it does?

Any ideas on this?   For the moment, I'm ignoring the issue, but I would like 
it better if I could isolate the VCPU's to a dedicated CPU in order to reduce 
measurement overhead in the guest.   (e. g. by forcing the trace daemon to 
run on CPU 0 and the measured guest to run on CPU 1.)

BTW, this is on changeset 13062.

-- 
Ray Bryant
AMD Performance Labs                   Austin, Tx
512-602-0038 (o)                 512-507-7807 (c)



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