From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1758906Ab2IEPoB (ORCPT <rfc822;w@1wt.eu>);
	Wed, 5 Sep 2012 11:44:01 -0400
Received: from mail-pb0-f46.google.com ([209.85.160.46]:32827 "EHLO
	mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1758848Ab2IEPn7 (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Wed, 5 Sep 2012 11:43:59 -0400
Message-ID: <50477332.1000902@gmail.com>
Date: Wed, 05 Sep 2012 09:43:46 -0600
From: David Ahern <dsahern@gmail.com>
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:14.0) Gecko/20120713 Thunderbird/14.0
MIME-Version: 1.0
To: Robert Richter <robert.richter@amd.com>,
        Peter Zijlstra <peterz@infradead.org>, Avi Kivity <avi@redhat.com>
CC: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
        Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Gleb Natapov <gleb@redhat.com>
Subject: Re: [PATCH 08/11] perf tool: precise mode requires exclude_guest
References: <1342826756-64663-1-git-send-email-dsahern@gmail.com> <1342826756-64663-9-git-send-email-dsahern@gmail.com> <20120723181358.GC6717@infradead.org> <500EAF23.8060909@gmail.com> <20120724161507.GG3732@erda.amd.com> <500EDB50.3070704@gmail.com> <20120724180312.GJ6717@infradead.org> <5010D2B1.3000206@gmail.com> <1343290109.26034.82.camel@twins> <20120803135117.GC3732@erda.amd.com>
In-Reply-To: <20120803135117.GC3732@erda.amd.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

In an attempt to jump start this thread...

On 8/3/12 7:51 AM, Robert Richter wrote:
> On 26.07.12 10:08:29, Peter Zijlstra wrote:
>> On Wed, 2012-07-25 at 23:16 -0600, David Ahern wrote:
>>
>>> Peter's patch (see https://lkml.org/lkml/2012/7/9/298) changes kernel
>>> side to require the use of exclude_guest if the precise modifier is
>>> used, returning -EOPNOTSUPP if exclude_guest is not set. This patch goes
>>> after the user experience: Today if a user specifies -e <event>:p all
>>> other modifiers are reset - including exclude_guest. Going forward we
>>> need :p to imply :pH if a user has not specified a GH modifer.
>>>
>>> We could do nothing and handle the unsupported error and try setting the
>>> exclude_guest option - like perf handles other new parameters. But
>>> EOPNOTSUPP is not uniquely tied to this error -- e.g., it could be the
>>> BTS is not supported (:pp). Also, we have no easy way to discriminate :p
>>> from :pG or :pGH. It seems to me perf should not silently undo a user
>>> request on the modifier, but inform the user the request is wrong. For
>>> example if a user request -e cycles:pG it should not be silently turned
>>> into :pH.
>>>
>>> And then yesterday, Robert stated that none of the exclude_xxxx
>>> modifiers can be set for the AMD if the precise modifier is used, so we
>>> cannot blindly set exclude_guest if precise_ip is set.
>>>
>>> So, seems to me perf need's one action for Intel processors and another
>>> for AMD.
>>
>> No, we just need to teach the IBS code about SVM enter/exit.
>
> I aggree that this could be emulated in software by enabling/disabling
> the event with a guest/host switch. And, even better, we add this for
> every pmu in a generic way. E.g. northbridge counter and I guess also
> Intel uncore events do not support G/H counting in hardware. Same to
> other pmus that could be imaginable in the future like counters for
> IOMMUs or other hardware devices.
>
> But, as some pmus are not related to virtualization or other features
> they simply do not need to support those attributes, or we want other
> defaults, e.g. enable it system wide. Detecting features with syscall
> error checking and then falling back to other defaults does not seem
> the right approach to me, because it may require several syscalls to
> check *combinations* of supported attributes, makes error logging and
> detection more difficult due to noisy log messages and because there
> is no strict attribute flag checking in current and older kernels.
>
> I better would like to see a pmu feature flag in the same style as
> with /proc/cpuinfo, e.g.:
>
>   $ cat /sys/bus/event_source/devices/cpu/flags
>   exclude_host exclude_guest
>
> We also need stricter attribute flag checking, esp. of reseved flags
> and for unsupported features in some pmus (I already work on some
> patches for this). Userland then checks flags and sets up syscalls
> according to the reported flags. The goal should be to avoid syscall
> errors at all. Thus, we are able to improve dmesg logging in case of
> errors, currently we do not see any message if a syscall fails.
>
> And finally, if a feature could be emulated, we could provide this
> emulation of an attr flag to all pmus.
>
> Does this make sense?

We need to require exclude_guest when using precise attribute with perf 
else all running VMs on Intel-based servers will crash. I do not have an 
AMD based server to even attempt the preferred solution. Best I can do 
is to attempt to keep this thread alive until someone with one can 
tackle the problem.

David