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Subject: Re: [PATCH 08/11] perf tool: precise mode requires exclude_guest
From: Peter Zijlstra <peterz@infradead.org>
To: David Ahern <dsahern@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        Robert Richter <robert.richter@amd.com>, 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>
Date: Thu, 26 Jul 2012 10:08:29 +0200
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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.