linux-kernel - Re: [PATCH] x86, perf, nmi: Disable perf if counters are not accessable

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Date:	Tue, 23 Nov 2010 22:04:18 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Don Zickus <dzickus@...hat.com>
Cc:	sedat.dilek@...il.com, LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] x86, perf, nmi: Disable perf if counters are not
	accessable

On Tue, Nov 23, 2010 at 07:27:07PM +0100, Peter Zijlstra wrote:
> On Tue, 2010-11-23 at 19:21 +0100, Sedat Dilek wrote:
> > Due to BIOS l(ocal)apic is not possible:
> > 
> > # dmesg | grep -i apic
> > [    0.000000] Using APIC driver default
> > [    0.000000] Local APIC disabled by BIOS -- you can enable it with "lapic"
> > [    0.000000] APIC: disable apic facility
> > [    0.000000] APIC: switched to apic NOOP
> > [    0.008891] no APIC, boot with the "lapic" boot parameter to force-enable it.
> > [    0.036141] Local APIC not detected. Using dummy APIC emulation. 
> 
> Have you tried booting with "lapic" as the second last msg suggests you
> do?

 Peter, Don, might not we need something like the patch below -- ie to check for
apic earlier and do not acquire cpu for PERF cpu bit, and its cpu model, etc
if there is no active apic? And perhaps for nmi-watchdog, we should not try
to creat perf event for same reason and simply report that nmi-watchdog is
disabled (though of course hpet based one should try to continue).

 No?

  Cyrill
---
 arch/x86/kernel/cpu/perf_event.c |   24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

Index: linux-2.6.git/arch/x86/kernel/cpu/perf_event.c
=====================================================================
--- linux-2.6.git.orig/arch/x86/kernel/cpu/perf_event.c
+++ linux-2.6.git/arch/x86/kernel/cpu/perf_event.c
@@ -1329,14 +1329,16 @@ x86_pmu_notifier(struct notifier_block *
 	return ret;
 }
 
-static void __init pmu_check_apic(void)
+static int __init pmu_check_apic(void)
 {
 	if (cpu_has_apic)
-		return;
+		return 0;
 
 	x86_pmu.apic = 0;
 	pr_info("no APIC, boot with the \"lapic\" boot parameter to force-enable it.\n");
 	pr_info("no hardware sampling interrupt available.\n");
+
+	return -1;
 }
 
 void __init init_hw_perf_events(void)
@@ -1346,6 +1348,10 @@ void __init init_hw_perf_events(void)
 
 	pr_info("Performance Events: ");
 
+	/* apic is required */
+	if (pmu_check_apic())
+		goto no_pmu;
+
 	switch (boot_cpu_data.x86_vendor) {
 	case X86_VENDOR_INTEL:
 		err = intel_pmu_init();
@@ -1356,12 +1362,8 @@ void __init init_hw_perf_events(void)
 	default:
 		return;
 	}
-	if (err != 0) {
-		pr_cont("no PMU driver, software events only.\n");
-		return;
-	}
-
-	pmu_check_apic();
+	if (err != 0)
+		goto no_pmu;
 
 	pr_cont("%s PMU driver.\n", x86_pmu.name);
 
@@ -1411,6 +1413,12 @@ void __init init_hw_perf_events(void)
 
 	perf_pmu_register(&pmu);
 	perf_cpu_notifier(x86_pmu_notifier);
+
+	return;
+
+no_pmu:
+	pr_cont("no PMU driver, software events only.\n");
+	return;
 }
 
 static inline void x86_pmu_read(struct perf_event *event)
--
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