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From: Anshuman Khandual <anshuman.khandual@arm.com>
To: linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, peterz@infradead.org,
	acme@kernel.org, mark.rutland@arm.com, will@kernel.org,
	catalin.marinas@arm.com
Cc: Mark Brown <broonie@kernel.org>,
	James Clark <james.clark@arm.com>, Rob Herring <robh@kernel.org>,
	Marc Zyngier <maz@kernel.org>,
	Suzuki Poulose <suzuki.poulose@arm.com>,
	Ingo Molnar <mingo@redhat.com>
Subject: Re: [PATCH V5 6/7] arm64/perf: Add BRBE driver
Date: Wed, 9 Nov 2022 08:38:31 +0530	[thread overview]
Message-ID: <c0401131-e0b4-7a25-8590-58402acb1e5b@arm.com> (raw)
In-Reply-To: <20221107062514.2851047-7-anshuman.khandual@arm.com>

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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  reply	other threads:[~2022-11-09  3:09 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-07  6:25 [PATCH V5 0/7] arm64/perf: Enable branch stack sampling Anshuman Khandual
2022-11-07  6:25 ` [PATCH V5 1/7] arm64/perf: Add BRBE registers and fields Anshuman Khandual
2022-11-07 15:15   ` Mark Brown
2022-11-07  6:25 ` [PATCH V5 2/7] arm64/perf: Update struct arm_pmu for BRBE Anshuman Khandual
2022-11-09 11:30   ` Suzuki K Poulose
2022-11-18  6:39     ` Anshuman Khandual
2022-11-18 17:47       ` Mark Rutland
2022-11-29  6:06         ` Anshuman Khandual
2022-11-07  6:25 ` [PATCH V5 3/7] arm64/perf: Update struct pmu_hw_events " Anshuman Khandual
2022-11-07  6:25 ` [PATCH V5 4/7] driver/perf/arm_pmu_platform: Add support for BRBE attributes detection Anshuman Khandual
2022-11-18 18:01   ` Mark Rutland
2022-11-21  6:36     ` Anshuman Khandual
2022-11-21 11:39       ` Mark Rutland
2022-11-28  8:24         ` Anshuman Khandual
2022-11-07  6:25 ` [PATCH V5 5/7] arm64/perf: Drive BRBE from perf event states Anshuman Khandual
2022-11-18 18:15   ` Mark Rutland
2022-11-29  6:26     ` Anshuman Khandual
2022-11-07  6:25 ` [PATCH V5 6/7] arm64/perf: Add BRBE driver Anshuman Khandual
2022-11-09  3:08   ` Anshuman Khandual [this message]
2022-11-16 16:42   ` James Clark
2022-11-17  5:45     ` Anshuman Khandual
2022-11-17 10:09       ` James Clark
2022-11-18  6:14         ` Anshuman Khandual
2022-11-29 15:53   ` James Clark
2022-11-30  4:49     ` Anshuman Khandual
2022-11-30 16:56       ` James Clark
2022-12-06 17:05       ` James Clark
2022-11-07  6:25 ` [PATCH V5 7/7] arm64/perf: Enable branch stack sampling Anshuman Khandual

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