From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Ahern <dsahern@gmail.com>
Subject: Re: perf CPU profiling in Xen guest fail & workaround
Date: Wed, 29 Jul 2015 14:02:23 -0600
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To: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: "linux-perf-use." <linux-perf-users@vger.kernel.org>

On 7/29/15 1:27 PM, Brendan Gregg wrote:
> Thanks, yes. This took me by surprise: I've been profiling different
> Xen guests for over a year, but this is the first time I've hit this.
>
> All my other Xen guests:
>
> # dmesg | grep Performance
> [    0.058664] Performance Events: unsupported p6 CPU model 62 no PMU
> driver, software events only.
>
> This linux 4.1 Xen guest:
>
> # dmesg | grep Performance
> [    0.258140] Performance Events: 16-deep LBR, IvyBridge events,
> Intel PMU driver.


yep and since the hypervisor lies perf has no means of knowing to 
fallback to cpu-clock.