linux-kernel - Re: [perfmon2] [PATCH] perf_events: AMD event scheduling (v3)

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Date:	Wed, 10 Feb 2010 17:07:13 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	"Drongowski, Paul" <paul.drongowski@....com>
Cc:	eranian@...il.com, Peter Zijlstra <peterz@...radead.org>,
	perfmon2-devel@...ts.sf.net, fweisbec@...il.com,
	linux-kernel@...r.kernel.org, paulus@...ba.org, mingo@...e.hu,
	davem@...emloft.net
Subject: Re: [perfmon2] [PATCH] perf_events: AMD event scheduling (v3)

On Wed, Feb 10, 2010 at 4:59 PM, Drongowski, Paul
<paul.drongowski@....com> wrote:
> Good catch!
>
> Historically, AMD has treated the bit field EventSelect<7:5>
> in model specific register MSRC001_00[03:00] Performance Event
> Select Register (PERF_CTL[3:0]) like an "event group selector".
> Please see the "BIOS and Kernel Developer's Guide for AMD
> Family 10h Processors."
>
> Typically, EventSelect<7:5> == 0x7 selects Northbridge
> events.
>
> Yes, when the event select value was extended to twelve bits,
> it placed this field somewhere in the middle of the full
> twelve bit value. ;-)
>
> Please consider AMD Family 10h event 0x1C0 Retired x87
> Floating Point Operations. This is not a Northbridge event.
> If the test is greater than or equal to (e.g., 0x1C0 >= 0x0E0),
> then this event will be incorrectly identified as a
> Northbridge event. (There are other similar examples.)
>
Good example.

> So, I would recommend testing EventSelect<7:5> == 0x7
> in order to detect AMD Northbridge events.
>
Ok, so something like the following would do it:

static inline int amd_is_nb_event(struct hw_perf_event *hwc)
{
   return (hwc->config >> 5) & 0x7 == 0x7;
}
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