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authorKan Liang <kan.liang@linux.intel.com>2020-01-27 08:53:54 -0800
committerIngo Molnar <mingo@kernel.org>2020-02-11 13:23:49 +0100
commitbbfd5e4fab63703375eafaf241a0c696024a59e1 (patch)
treed3710969e9950bdcf7fe048ce3fd23bbe622dba7 /arch/x86/events
parent6c1c07b33eb093e5a2a313ece89baa596ba6135e (diff)
downloadlinux-bbfd5e4fab63703375eafaf241a0c696024a59e1.tar.gz
perf/core: Add new branch sample type for HW index of raw branch records
The low level index is the index in the underlying hardware buffer of the most recently captured taken branch which is always saved in branch_entries[0]. It is very useful for reconstructing the call stack. For example, in Intel LBR call stack mode, the depth of reconstructed LBR call stack limits to the number of LBR registers. With the low level index information, perf tool may stitch the stacks of two samples. The reconstructed LBR call stack can break the HW limitation. Add a new branch sample type to retrieve low level index of raw branch records. The low level index is between -1 (unknown) and max depth which can be retrieved in /sys/devices/cpu/caps/branches. Only when the new branch sample type is set, the low level index information is dumped into the PERF_SAMPLE_BRANCH_STACK output. Perf tool should check the attr.branch_sample_type, and apply the corresponding format for PERF_SAMPLE_BRANCH_STACK samples. Otherwise, some user case may be broken. For example, users may parse a perf.data, which include the new branch sample type, with an old version perf tool (without the check). Users probably get incorrect information without any warning. Signed-off-by: Kan Liang <kan.liang@linux.intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lkml.kernel.org/r/20200127165355.27495-2-kan.liang@linux.intel.com
Diffstat (limited to 'arch/x86/events')
-rw-r--r--arch/x86/events/intel/lbr.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
index 534c76606049..7639e2097101 100644
--- a/arch/x86/events/intel/lbr.c
+++ b/arch/x86/events/intel/lbr.c
@@ -585,6 +585,7 @@ static void intel_pmu_lbr_read_32(struct cpu_hw_events *cpuc)
cpuc->lbr_entries[i].reserved = 0;
}
cpuc->lbr_stack.nr = i;
+ cpuc->lbr_stack.hw_idx = -1ULL;
}
/*
@@ -680,6 +681,7 @@ static void intel_pmu_lbr_read_64(struct cpu_hw_events *cpuc)
out++;
}
cpuc->lbr_stack.nr = out;
+ cpuc->lbr_stack.hw_idx = -1ULL;
}
void intel_pmu_lbr_read(void)
@@ -1120,6 +1122,7 @@ void intel_pmu_store_pebs_lbrs(struct pebs_lbr *lbr)
int i;
cpuc->lbr_stack.nr = x86_pmu.lbr_nr;
+ cpuc->lbr_stack.hw_idx = -1ULL;
for (i = 0; i < x86_pmu.lbr_nr; i++) {
u64 info = lbr->lbr[i].info;
struct perf_branch_entry *e = &cpuc->lbr_entries[i];