Hi Leo,
在 2023/8/14 16:47, Leo Yan 写道:
Hi Shijie,
On Mon, Aug 14, 2023 at 04:12:23PM +0800, Shijie Huang wrote:
[...]
Their investigation indicates that upon counter rotation (which
takes place on the back of a timer interrupt), we fail to
re-apply the guest EL0 enabling, leading to the counting of host
events instead of guest events.
Seems to me, it's not clear for why the counter rotation will cause
the issue.
In the example shared by Shijie in [1], the cycle counter is enabled for
both host and guest, and cycle counter is a dedicated event which does
not share counter with other events. Even there have counter rotation,
it should not impact the cycle counter.
Just take a simple case:
perf stat -e cycles:G,cycles:H, e2,e3,e4,e5,e6,e7 ....
Assume we have 8 events, but PMU only privides 7 counters(cycle + 6 normal)
Thanks for the detailed info, now I understand it.
Seems to me, based on Marc's patch, we need to apply below change. In
below code, we don't need to change the perf core code and we can
resolve it as a common issue for Arm PMU drivers.
diff --git a/arch/arm64/kvm/pmu.c b/arch/arm64/kvm/pmu.c
index 121f1a14c829..8f9673cdadec 100644
--- a/arch/arm64/kvm/pmu.c
+++ b/arch/arm64/kvm/pmu.c
@@ -38,14 +38,20 @@ struct kvm_pmu_events *kvm_get_pmu_events(void)
void kvm_set_pmu_events(u32 set, struct perf_event_attr *attr)
{
struct kvm_pmu_events *pmu = kvm_get_pmu_events();
+ int resync;
if (!kvm_arm_support_pmu_v3() || !pmu || !kvm_pmu_switch_needed(attr))
return;
+ resync = pmu->events_guest != set;
If we set two events in guest, the resync will set
For example:
perf stat -e cycles:Gu, cycles:Gk
If so, this is not reasonble...
Thanks
Huang Shijie
+
if (!attr->exclude_host)
pmu->events_host |= set;
if (!attr->exclude_guest)
pmu->events_guest |= set;
+
+ if (resync)
+ kvm_vcpu_pmu_resync_el0();
}
/*
@@ -60,6 +66,8 @@ void kvm_clr_pmu_events(u32 clr)
pmu->events_host &= ~clr;
pmu->events_guest &= ~clr;
+
+ kvm_vcpu_pmu_resync_el0();
}
