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Subject[tip: perf/core] perf/x86: Fix n_pair for cancelled txn
The following commit has been merged into the perf/core branch of tip:

Commit-ID: 871a93b0aad65a7f44ee25f2d17932ef6d559850
Gitweb: https://git.kernel.org/tip/871a93b0aad65a7f44ee25f2d17932ef6d559850
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Mon, 05 Oct 2020 10:09:06 +02:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 06 Oct 2020 15:18:17 +02:00

perf/x86: Fix n_pair for cancelled txn

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@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Kim Phillips <kim.phillips@amd.com>
Link: https://lkml.kernel.org/r/20201005082516.GG2628@hirez.programming.kicks-ass.net
---
arch/x86/events/core.c | 6 +++++-
arch/x86/events/perf_event.h | 1 +
2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index cb5cfef..a7248a3 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -1064,8 +1064,10 @@ static int collect_event(struct cpu_hw_events *cpuc, struct perf_event *event,
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;
}
@@ -2006,6 +2008,7 @@ static void x86_pmu_start_txn(struct pmu *pmu, unsigned int txn_flags)

perf_pmu_disable(pmu);
__this_cpu_write(cpu_hw_events.n_txn, 0);
+ __this_cpu_write(cpu_hw_events.n_txn_pair, 0);
}

/*
@@ -2031,6 +2034,7 @@ static void x86_pmu_cancel_txn(struct pmu *pmu)
*/
__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);
}

diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index 3454424..93e56d7 100644
--- 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];

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