On 30/9/2021 4:05 am, Song Liu wrote:
Hi Kan,
On Sep 29, 2021, at 9:35 AM, Liang, Kan <kan.liang@xxxxxxxxx> wrote:
- get confirmation that clearing GLOBAL_CTRL is suffient to supress
PEBS, in which case we can simply remove the PEBS_ENABLE clear.
How should we confirm this? Can we run some tests for this? Or do we
need hardware experts' input for this?
I'll put it on the list to ask the hardware people when I talk to them next. But
maybe Kan or Andi know without asking.
If the GLOBAL_CTRL is explicitly disabled, the counters do not count anymore.
It doesn't matter if PEBS is enabled or not.
See 6c1c07b33eb0 ("perf/x86/intel: Avoid unnecessary PEBS_ENABLE MSR
access in PMI "). We optimized the PMU handler base on it.
Thanks for these information!
IIUC, all we need is the following on top of bpf-next/master:
diff --git i/arch/x86/events/intel/core.c w/arch/x86/events/intel/core.c
index 1248fc1937f82..d0d357e7d6f21 100644
--- i/arch/x86/events/intel/core.c
+++ w/arch/x86/events/intel/core.c
@@ -2209,7 +2209,6 @@ intel_pmu_snapshot_branch_stack(struct perf_branch_entry *entries, unsigned int
/* must not have branches... */
local_irq_save(flags);
__intel_pmu_disable_all(false); /* we don't care about BTS */
If the value passed in is true, does it affect your use case?
- __intel_pmu_pebs_disable_all();
In that case, we can reuse "static __always_inline void intel_pmu_disable_all(void)"
regardless of whether PEBS is supported or enabled inside the guest and the host ?
__intel_pmu_lbr_disable();
How about using intel_pmu_lbr_disable_all() to cover Arch LBR?
/* ... until here */
return __intel_pmu_snapshot_branch_stack(entries, cnt, flags);
@@ -2223,7 +2222,6 @@ intel_pmu_snapshot_arch_branch_stack(struct perf_branch_entry *entries, unsigned
/* must not have branches... */
local_irq_save(flags);
__intel_pmu_disable_all(false); /* we don't care about BTS */
- __intel_pmu_pebs_disable_all();
__intel_pmu_arch_lbr_disable();
/* ... until here */
return __intel_pmu_snapshot_branch_stack(entries, cnt, flags);
In the test, this does eliminate the warning.
Thanks,
Song
