[PATCH] perf/x86: Fix n_pair for cancelled txn

[Peter Zijlstra]

On Fri, Oct 02, 2020 at 04:10:42PM -0500, Kim Phillips wrote:
> Tested-by: Kim Phillips <kim.phillips@xxxxxxx>

---
Subject: perf/x86: Fix n_pair for cancelled txn
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Mon Oct  5 10:09:06 CEST 2020

Kan reported that n_metric gets corrupted for cancelled transactions;
a similar issue exists for n_pair for AMD's Large Increment thing.

The problem was confirmed and confirmed fixed by Kim using:

  sudo perf stat -e "{cycles,cycles,cycles,cycles}:D" -a sleep 10 &

  # should succeed:
  sudo perf stat -e "{fp_ret_sse_avx_ops.all}:D" -a workload

  # should fail:
  sudo perf stat -e "{fp_ret_sse_avx_ops.all,fp_ret_sse_avx_ops.all,cycles}:D" -a workload

  # previously failed, now succeeds with this patch:
  sudo perf stat -e "{fp_ret_sse_avx_ops.all}:D" -a workload

Fixes: 5738891229a2 ("perf/x86/amd: Add support for Large Increment per Cycle Events")
Reported-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Tested-by: Kim Phillips <kim.phillips@xxxxxxx>
---
 arch/x86/events/core.c       |    6 +++++-
 arch/x86/events/perf_event.h |    1 +
 2 files changed, 6 insertions(+), 1 deletion(-)

--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -1089,8 +1089,10 @@ static int collect_event(struct cpu_hw_e
 		return -EINVAL;
 
 	cpuc->event_list[n] = event;
-	if (is_counter_pair(&event->hw))
+	if (is_counter_pair(&event->hw)) {
 		cpuc->n_pair++;
+		cpuc->n_txn_pair++;
+	}
 
 	return 0;
 }
@@ -2062,6 +2064,7 @@ static void x86_pmu_start_txn(struct pmu
 
 	perf_pmu_disable(pmu);
 	__this_cpu_write(cpu_hw_events.n_txn, 0);
+	__this_cpu_write(cpu_hw_events.n_txn_pair, 0);
 }
 
 /*
@@ -2087,6 +2090,7 @@ static void x86_pmu_cancel_txn(struct pm
 	 */
 	__this_cpu_sub(cpu_hw_events.n_added, __this_cpu_read(cpu_hw_events.n_txn));
 	__this_cpu_sub(cpu_hw_events.n_events, __this_cpu_read(cpu_hw_events.n_txn));
+	__this_cpu_sub(cpu_hw_events.n_pair, __this_cpu_read(cpu_hw_events.n_txn_pair));
 	perf_pmu_enable(pmu);
 }
 
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -235,6 +235,7 @@ struct cpu_hw_events {
 					     they've never been enabled yet */
 	int			n_txn;    /* the # last events in the below arrays;
 					     added in the current transaction */
+	int			n_txn_pair;
 	int			assign[X86_PMC_IDX_MAX]; /* event to counter assignment */
 	u64			tags[X86_PMC_IDX_MAX];