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

Peter Zijlstra
2010-11-23T19:07:37Z

On Tue, 2010-11-23 at 22:04 +0300, Cyrill Gorcunov wrote:
> 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?
>

Ah, no.. now I get what you mean.

We can use the pmu without interrupt with we miss the lapic, that is
perf-stat will still work.

> 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;
> +

> +no_pmu:
> + pr_cont("no PMU driver, software events only.\n");
> + return;
> }
>
> static inline void x86_pmu_read(struct perf_event *event)