linux-kernel - Re: [PATCH] perf, ibs: Check syscall attribute flags

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Message-ID: <20120907172505.GM8285@erda.amd.com>
Date:	Fri, 7 Sep 2012 19:25:05 +0200
From:	Robert Richter <robert.richter@....com>
To:	David Ahern <dsahern@...il.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf, ibs: Check syscall attribute flags

On 07.09.12 11:11:56, David Ahern wrote:
> On 9/7/12 11:07 AM, Robert Richter wrote:
> >> Am I reading this right - if exclude_guest is set then perf_ibs_init
> >> returns -EINVAL?
> >
> > Yes, the hardware does not support this. I will look for a solution
> > which emulates this is software.
> 
> ugh, that's exactly we need for Intel: if precise is set, exclude_guest 
> must be set.
> 
> In perf I would like to set exclude_guest if precise is set -- what I 
> mentioned yesterday for the patch https://lkml.org/lkml/2012/7/20/437. 
> With my patch -e cycles:p on AMD will then fail EINVAL.

You may set this bit per default. On EINVAL perf falls back and clears
the bit. I tested exactly this for ibs and it works.

So, on Intel, if the guest_exclude bit is not set, the kernel simply
throws an EINVAL too, but since perf sets it per default with the
precise modifier there shouldn't be any problem here.

-Robert

-- 
Advanced Micro Devices, Inc.
Operating System Research Center

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