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

Cyrill Gorcunov
2010-11-23T19:04:24Z

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)