On Thu, Aug 07, 2014 at 10:03:58AM +0100, Anup Patel wrote: > On 6 August 2014 19:54, Will Deacon <will.deacon@xxxxxxx> wrote: > > On Tue, Aug 05, 2014 at 10:24:11AM +0100, Anup Patel wrote: > >> A hypervisor will typically mask the overflow interrupt before > >> forwarding it to Guest Linux hence we need to re-enable the overflow > >> interrupt after clearing it in Guest Linux. Also, this re-enabling > >> of overflow interrupt does not harm in non-virtualized scenarios. > >> > >> Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@xxxxxxxxxx> > >> Signed-off-by: Anup Patel <anup.patel@xxxxxxxxxx> > >> --- > >> arch/arm64/kernel/perf_event.c | 8 ++++++++ > >> 1 file changed, 8 insertions(+) > >> > >> diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c > >> index 47dfb8b..19fb140 100644 > >> --- a/arch/arm64/kernel/perf_event.c > >> +++ b/arch/arm64/kernel/perf_event.c > >> @@ -1076,6 +1076,14 @@ static irqreturn_t armv8pmu_handle_irq(int irq_num, void *dev) > >> if (!armv8pmu_counter_has_overflowed(pmovsr, idx)) > >> continue; > >> > >> + /* > >> + * If we are running under a hypervisor such as KVM then > >> + * hypervisor will mask the interrupt before forwarding > >> + * it to Guest Linux hence re-enable interrupt for the > >> + * overflowed counter. > >> + */ > >> + armv8pmu_enable_intens(idx); > >> + > > > > Really? This is a giant bodge in the guest to work around short-comings in > > the hypervisor. Why can't we fix this properly using something like Marc's > > irq forwarding code? > > This change is in accordance with our previous RFC thread about > PMU virtualization where Marc Z had suggest to do interrupt > mask/unmask dance similar to arch-timer. > > I have not tried Marc'z irq forwarding series. In next revision of this > patchset, I will try to use Marc's irq forwarding approach. That would be good. Judging by the colour Marc went when he saw this patch, I don't think he intended you to hack perf in this way :) Will -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
