linux-kernel - Re: [PATCH] oprofile, x86: Fix race in nmi handler while starting

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Message-ID: <20110617080618.GA893@elte.hu>
Date:	Fri, 17 Jun 2011 10:06:18 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Robert Richter <robert.richter@....com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	oprofile-list <oprofile-list@...ts.sourceforge.net>,
	"Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>
Subject: Re: [PATCH] oprofile, x86: Fix race in nmi handler while starting


* Robert Richter <robert.richter@....com> wrote:

> On 09.06.11 03:18:54, Ingo Molnar wrote:
> > 
> > * Robert Richter <robert.richter@....com> wrote:
> > 
> > > In some rare cases, nmis are generated immediately after the 
> > > nmi handler of the cpu was started. This causes the counter not 
> > > to be enabled. Before enabling the nmi handlers we need to set 
> > > variable ctr_running first and make sure its value is written 
> > > to memory.
> > > 
> > > Also, the patch makes all existing barriers a memory barrier 
> > > instead of a compiler barrier only.
> > 
> > Could we *PLEASE* just do the obvious and turn oprofile into a 
> > perf user on x86 too, like ARM already does? Two years down the 
> > line and there's zero progress in that area. We want to obsolete 
> > the Oprofile PMU bits on x86, the infrastructure duplication 
> > causes non-trivial problems like this one.
> 
> Ingo,
> 
> I would rather prefer to spend the effort to add full pmu support 
> to perf. AMD features missing are still IBS and nb performance 
> counters for family 15h. The oprofile kernel driver would become 
> obsolete at all with a new daemon using the perf syscall interface.

Agreed - i just don't see *any* progress on the IBS front: more time 
seems to be spent on fixing and sometimes even extending oprofile 
than on any IBS work.

Thanks,

	Ingo
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