linux-kernel - [PATCH] perf_events: fix bug in AMD per-cpu initialization

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Date:	Wed, 24 Mar 2010 15:45:01 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	linux-kernel@...r.kernel.org
Cc:	peterz@...radead.org, mingo@...e.hu, paulus@...ba.org,
	davem@...emloft.net, fweisbec@...il.com, robert.richter@....com,
	perfmon2-devel@...ts.sf.net, eranian@...il.com, eranian@...gle.com,
	hpa@...or.com, tglx@...utronix.de, manfred@...orfullife.com
Subject: [PATCH] perf_events: fix bug in AMD per-cpu initialization

> Crap, you're right, either notify_cpu_starting() is done too early or
> smp_store_cpu_info() is done too late.
> 
> Since smp_store_cpu_info() relies on the result of calibrate_delay() we
> can't easily change that order, but since there really isn't any other
> CPU_STARTING user in tree (I appear to have created the first?!) we can
> easily move that notifier thing later.
> 
> (What's up with that IRQ-enable over calibrate_delay(), can't we simply
> enable the NMI watchdog later?)
> 
> So I guess something like the below should work:

The patch does work for me. I made two small modifications by
adding amd_has_nb() such that the correct checking is for on amd_nb.

	Signed-off-by: Stephane Eranian <eranian@...gle.com>

diff --git a/arch/x86/kernel/cpu/perf_event_amd.c b/arch/x86/kernel/cpu/perf_event_amd.c
index a61e54b..6204739 100644
--- a/arch/x86/kernel/cpu/perf_event_amd.c
+++ b/arch/x86/kernel/cpu/perf_event_amd.c
@@ -137,6 +137,13 @@ static inline int amd_is_nb_event(struct hw_perf_event *hwc)
 	return (hwc->config & 0xe0) == 0xe0;
 }
 
+static inline int amd_has_nb(struct cpu_hw_events *cpuc)
+{
+	struct amd_nb *nb = cpuc->amd_nb;
+
+	return nb && nb->nb_id != -1;
+}
+
 static void amd_put_event_constraints(struct cpu_hw_events *cpuc,
 				      struct perf_event *event)
 {
@@ -147,7 +154,7 @@ static void amd_put_event_constraints(struct cpu_hw_events *cpuc,
 	/*
 	 * only care about NB events
 	 */
-	if (!(nb && amd_is_nb_event(hwc)))
+	if (!(amd_has_nb(cpuc) && amd_is_nb_event(hwc)))
 		return;
 
 	/*
@@ -214,7 +221,7 @@ amd_get_event_constraints(struct cpu_hw_events *cpuc, struct perf_event *event)
 	/*
 	 * if not NB event or no NB, then no constraints
 	 */
-	if (!(nb && amd_is_nb_event(hwc)))
+	if (!(amd_has_nb(cpuc) && amd_is_nb_event(hwc)))
 		return &unconstrained;
 
 	/*
--
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