Re: [GIT PULL] perf changes for v3.8
[Posted December 19, 2012 by jake]
| From: |
| David Ahern <dsahern-AT-gmail.com> |
| To: |
| Linus Torvalds <torvalds-AT-linux-foundation.org> |
| Subject: |
| Re: [GIT PULL] perf changes for v3.8 |
| Date: |
| Wed, 12 Dec 2012 20:43:09 -0700 |
| Message-ID: |
| <50C94ECD.6020504@gmail.com> |
| Cc: |
| Ingo Molnar <mingo-AT-kernel.org>,
Linux Kernel Mailing List <linux-kernel-AT-vger.kernel.org>,
Arnaldo Carvalho de Melo <acme-AT-infradead.org>,
Peter Zijlstra <a.p.zijlstra-AT-chello.nl>,
Thomas Gleixner <tglx-AT-linutronix.de>,
Andrew Morton <akpm-AT-linux-foundation.org> |
| Archive‑link: | |
Article |
On 12/12/12 8:34 PM, Linus Torvalds wrote:
> On Wed, Dec 12, 2012 at 7:25 PM, David Ahern <dsahern@gmail.com> wrote:
>>
>> Are you running an older perf binary on the 3.8 kernel?
>
> I am.. I don't tend to rebuild 'perf'..
>
>> Does this work: perf record -e cycles:ppH ...
>
> Yes it does. What is 'H' and why should anybody care? Especially since
> I'm not running virtualized.
>
> That whole "exclude_guest" test is insane when there isn't any
> virtualization going on. Very annoying.
you know what's worse? All of your VMs blowing up because anyone runs
perf with precise attribute. Virtualization and and performance
monitoring collide. From the log message for commit 1342798.
"Intel PEBS in VT-x context uses the DS address as a guest linear
address, even though its programmed by the host as a host linear
address. This either results in guest memory corruption and or the
hardware faulting and 'crashing' the virtual machine. Therefore we have
to disable PEBS on VT-x enter and re-enable on VT-x exit, enforcing a
strict exclude_guest."
David
