From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: boot_cpu_data differs between Xen hypervisor boot
	and normal pv_ops kernel boot
Date: Wed, 31 Mar 2010 11:14:10 -0700
Message-ID: <4BB390F2.8080206@goop.org>
References: <4BB36A40.1080903@purdue.edu>
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To: Naresh Rapolu <nrapolu@purdue.edu>
Cc: xen-devel@lists.xensource.com, Stephen Spector <stephen.spector@citrix.com>
List-Id: xen-devel@lists.xenproject.org

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.)

     J