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Date: Fri, 29 Apr 2011 20:17:24 +0300
Message-ID: <BANLkTimjmYUJMGw0aB+w+E76H+kxSpqFZg@mail.gmail.com>
Subject: Re: re-enable Nehalem raw Offcore-Events support
From: Pekka Enberg <penberg@kernel.org>
To: Vince Weaver <vweaver1@eecs.utk.edu>
Cc: torvalds@linux-foundation.org, Ingo Molnar <mingo@elte.hu>,
        linux-kernel@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
        Stephane Eranian <eranian@gmail.com>, Andi Kleen <ak@linux.intel.com>
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Hi Vince,

On Fri, Apr 29, 2011 at 6:04 PM, Vince Weaver <vweaver1@eecs.utk.edu> wrote:
> Hello Linus
>
> can you revert the commit b52c55c6a25e4515b5e075a989ff346fc251ed09
>
> This removed functionality from perf_events that allowed raw event access
> for OFFCORE_EVENTS type events on Nehalem and Westmere cpus.
>
> To be fair, this is not technically a regression as the feature was only
> (finally!) added in the 2.6.39 merge window. ?However this is a useful
> feature and many tools (including the PAPI performance counter library
> that I work on) had added support for it in anticipation of the 2.6.39
> release.
>
> Ingo's reasons for removing the feature seem to boil down to
> ?1. ?"perf" doesn't use the functionality, and any other userspace
> ? ? ?program that uses the perf_events syscalls don't matter
> ?2. ?Users are too stupid to use the raw functionality properly;
> ? ? ?we should only allow a kernel-developer-approved small subset
> ? ? ?of the features provided by the CPU as described in the intel
> ? ? ?developers manuals.
>
> #2 seems like a gross misinterpretation of the whole "Linux gives you
> enough rope to shoot yourself in the foot" policy from days passed, but
> maybe things have moved on.

That's a gross misrepresentation of what Ingo has been saying on LKML.
Really, learn to work with relevant maintainers before you ask Linus
to revert something.

                                Pekka
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