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Re: [Xen-devel] boot_cpu_data differs between Xen hypervisor boot and no

To: Naresh Rapolu <nrapolu@xxxxxxxxxx>
Subject: Re: [Xen-devel] boot_cpu_data differs between Xen hypervisor boot and normal pv_ops kernel boot
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Wed, 31 Mar 2010 11:14:10 -0700
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Stephen Spector <stephen.spector@xxxxxxxxxx>
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On 03/31/2010 08:29 AM, Naresh Rapolu wrote:

When I looked into the source code, arch/x86/kernel/cpu/perf_event.c, at run-time boot_cpu_data structure seems to differ in these two forms of booting. Due to this, Iam not able to use the hardware performance counters in my Xeon 5530 processor as hardware events(cache-misses etc) are being disabled.

Is there any reason for this ?

The PMU hardware features are not virtualized, and are not available to guest domains. I don't think Xen has much of a useful API to expose these features, though oprofile was working at one point.

I agree it would be very useful to work out how to get good "perf" support in a Xen domain.

(Stephen: It might be an interesting SoC project.)


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