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Date: Wed, 9 Nov 2022 08:38:31 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, peterz@...radead.org,
acme@...nel.org, mark.rutland@....com, will@...nel.org,
catalin.marinas@....com
Cc: Mark Brown <broonie@...nel.org>, James Clark <james.clark@....com>,
Rob Herring <robh@...nel.org>, Marc Zyngier <maz@...nel.org>,
Suzuki Poulose <suzuki.poulose@....com>,
Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH V5 6/7] arm64/perf: Add BRBE driver
On 11/7/22 11:55, Anshuman Khandual wrote:
> +void arm64_pmu_brbe_read(struct pmu_hw_events *cpuc, struct perf_event *event)
> +{
> + u64 brbinf;
> + int idx;
> +
> + if (brbe_disabled(cpuc))
> + return;
> +
> + set_brbe_paused();
> + for (idx = 0; idx < cpuc->brbe_nr; idx++) {
> + select_brbe_bank_index(idx);
> + brbinf = get_brbinf_reg(idx);
> + /*
> + * There are no valid entries anymore on the buffer.
> + * Abort the branch record processing to save some
> + * cycles and also reduce the capture/process load
> + * for the user space as well.
> + */
> + if (brbe_invalid(brbinf))
> + break;
> +
> + if (brbe_valid(brbinf)) {
> + cpuc->branches->brbe_entries[idx].from = get_brbsrc_reg(idx);
> + cpuc->branches->brbe_entries[idx].to = get_brbtgt_reg(idx);
> + } else if (brbe_source(brbinf)) {
> + cpuc->branches->brbe_entries[idx].from = get_brbsrc_reg(idx);
> + cpuc->branches->brbe_entries[idx].to = 0;
> + } else if (brbe_target(brbinf)) {
> + cpuc->branches->brbe_entries[idx].from = 0;
> + cpuc->branches->brbe_entries[idx].to = get_brbtgt_reg(idx);
> + }
> + capture_brbe_flags(cpuc, event, brbinf, idx);
> + }
> + cpuc->branches->brbe_stack.nr = idx;
> + cpuc->branches->brbe_stack.hw_idx = -1ULL;
> + process_branch_aborts(cpuc);
> +}
The following additional changes are required to ensure that BRBE remains "un-paused" after
processing the branch records inside PMU interrupt handler. Without this change, there will
PMU interrupts without valid branch records, reducing branch stack sample collection during
given workload execution. I will fold this into the BRBE driver.
diff --git a/drivers/perf/arm_pmu_brbe.c b/drivers/perf/arm_pmu_brbe.c
index ce1aa4171481..c8154ddd341d 100644
--- a/drivers/perf/arm_pmu_brbe.c
+++ b/drivers/perf/arm_pmu_brbe.c
@@ -429,6 +429,7 @@ void arm64_pmu_brbe_read(struct pmu_hw_events *cpuc, struct perf_event *event)
cpuc->branches->brbe_stack.nr = idx;
cpuc->branches->brbe_stack.hw_idx = -1ULL;
process_branch_aborts(cpuc);
+ clr_brbe_paused();
}
void arm64_pmu_brbe_reset(struct pmu_hw_events *cpuc)
diff --git a/drivers/perf/arm_pmu_brbe.h b/drivers/perf/arm_pmu_brbe.h
index 22c4b25b1777..33da6fc9aefa 100644
--- a/drivers/perf/arm_pmu_brbe.h
+++ b/drivers/perf/arm_pmu_brbe.h
@@ -257,3 +257,11 @@ static inline void set_brbe_paused(void)
write_sysreg_s(brbfcr | BRBFCR_EL1_PAUSED, SYS_BRBFCR_EL1);
isb();
}
+
+static inline void clr_brbe_paused(void)
+{
+ u64 brbfcr = read_sysreg_s(SYS_BRBFCR_EL1);
+
+ write_sysreg_s(brbfcr & ~BRBFCR_EL1_PAUSED, SYS_BRBFCR_EL1);
+ isb();
+}
For example:
./perf record -j any,u,k,save_type ls
./perf report -D | grep branch
Before this change -
# cat out | grep "branch stack: nr:64" | wc -l
4
# cat out | grep "branch stack: nr:0" | wc -l
57
# perf report -D | grep branch
... branch stack: nr:64
... branch stack: nr:0
... branch stack: nr:64
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:64
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:64
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
... branch stack: nr:0
But after this change -
$ cat out | grep "branch stack: nr:64" | wc -l
107
# cat out | grep "branch stack: nr:0" | wc -l
0
$ perf report -D | grep branch
.......................
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
... branch stack: nr:64
.......................
- Anshuman
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