diff options
Diffstat (limited to 'arch/x86/kernel/cpu/perf_event_p4.c')
| -rw-r--r-- | arch/x86/kernel/cpu/perf_event_p4.c | 17 |
1 files changed, 13 insertions, 4 deletions
diff --git a/arch/x86/kernel/cpu/perf_event_p4.c b/arch/x86/kernel/cpu/perf_event_p4.c index d1f77e2..e93fcd5 100644 --- a/arch/x86/kernel/cpu/perf_event_p4.c +++ b/arch/x86/kernel/cpu/perf_event_p4.c @@ -950,11 +950,20 @@ static int p4_pmu_handle_irq(struct pt_regs *regs) x86_pmu_stop(event, 0); } - if (handled) { - /* p4 quirk: unmask it again */ - apic_write(APIC_LVTPC, apic_read(APIC_LVTPC) & ~APIC_LVT_MASKED); + if (handled) inc_irq_stat(apic_perf_irqs); - } + + /* + * When dealing with the unmasking of the LVTPC on P4 perf hw, it has + * been observed that the OVF bit flag has to be cleared first _before_ + * the LVTPC can be unmasked. + * + * The reason is the NMI line will continue to be asserted while the OVF + * bit is set. This causes a second NMI to generate if the LVTPC is + * unmasked before the OVF bit is cleared, leading to unknown NMI + * messages. + */ + apic_write(APIC_LVTPC, APIC_DM_NMI); return handled; } |