linux-kernel - Re: [perfmon] Re: [PATCH 1/2] Separate the performance counter allocation from the LAPIC NMI watchdog

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Date:	Fri, 22 Jun 2007 03:02:38 -0700
From:	Stephane Eranian <eranian@....hp.com>
To:	Björn Steinbrink <B.Steinbrink@....de>,
	Andi Kleen <ak@...e.de>, mingo@...e.hu,
	linux-kernel@...r.kernel.org, levon@...ementarian.org,
	perfmon@...ali.hpl.hp.com, oprofile-list@...ts.sourceforge.net,
	wcohen@...hat.com, akpm@...ux-foundation.org
Subject: Re: [perfmon] Re: [PATCH 1/2] Separate the performance counter allocation from the LAPIC NMI watchdog

Bjorn,

You have the following registers to consider (for P4/Core):

#define MSR_IA32_PEBS_ENABLE            0x000003f1
#define MSR_CORE_PERF_FIXED_CTR0        0x00000309
#define MSR_CORE_PERF_FIXED_CTR1        0x0000030a
#define MSR_CORE_PERF_FIXED_CTR2        0x0000030b
#define MSR_CORE_PERF_FIXED_CTR_CTRL    0x0000038d
#define MSR_CORE_PERF_GLOBAL_STATUS     0x0000038e
#define MSR_CORE_PERF_GLOBAL_CTRL       0x0000038f
#define MSR_CORE_PERF_GLOBAL_OVF_CTRL   0x00000390


With Barcelona, you'll also have to consider:

#define MSR_AMD64_IBSFETCHCTL           0xc0011030
#define MSR_AMD64_IBSFETCHLINAD         0xc0011031
#define MSR_AMD64_IBSFETCHPHYSAD        0xc0011032
#define MSR_AMD64_IBSOPCTL              0xc0011033
#define MSR_AMD64_IBSOPRIP              0xc0011034
#define MSR_AMD64_IBSOPDATA             0xc0011035
#define MSR_AMD64_IBSOPDATA2            0xc0011036
#define MSR_AMD64_IBSOPDATA3            0xc0011037
#define MSR_AMD64_IBSDCLINAD            0xc0011038
#define MSR_AMD64_IBSDCPHYSAD           0xc0011039
#define MSR_AMD64_IBSCTL                0xc001103A

I think you could organize by groups with a bitmap 
per group and some sorted linked list to keep track
of all of them.


On Fri, Jun 22, 2007 at 09:13:54AM +0200, Bj?rn Steinbrink wrote:
> Hi Stephane,
> 
> On 2007.06.21 01:36:45 -0700, Stephane Eranian wrote:
> > Bjorn,
> > 
> > 
> > On Wed, Jun 20, 2007 at 02:59:33PM -0700, Stephane Eranian wrote:
> > > Bjorn,
> > > 
> > > I ran into one issue related with the new allocator.
> 
> Should be the same with 2.6.21 and earlier, the "new" allocator should
> do exactly the samething, it just fixes the breakage introduced in the
> post-2.6.21 cleanup.
> 
> > > In the case of a Core 2 Duo processor, the PMU implements more
> > > than just basic counters. In particular it supports fixed counters
> > > and PEBS where both use another set of MSRs. Those are not within
> > > a 66 bit distance from MSR_ARCH_PERFMON_EVNTSEL0. Thus the allocator
> > > fails with an assertion.
> 
> How far away are they?
> 
> > > 
> > > I do know that perfmon is the only consumer of those extended 
> > > features TODAY. Yet I think we need to define the allocator such
> > > that it can work with other "distant" MSRs as well.
> > > 
> > 
> > I think that a workaround for this issue could be for the allocator
> > to grant the requests for registers outside of the range, i.e., register
> > that it does not see/manage.
> 
> That would also allow multiple subsystems to use them at the same time.
> And whoever adds the second user of those MSRs might not be aware of the
> just-grant-it policy of the allocator. And bugs that arise due to such
> problems will probably become a real PITA to track down.
> 
> Unfortunately, I don't see any elegant solution to this atm, and of
> course making your code simply circumvent the allocator isn't an option
> either.
> 
> Thanks,
> Björn
> 
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-- 

-Stephane
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