The following commit has been merged into the perf/core branch of tip:
Commit-ID: 0bc3be5b4bfd5b75086c26d63584a6f7aaea87d5
Gitweb: https://git.kernel.org/tip/0bc3be5b4bfd5b75086c26d63584a6f7aaea87d5
Author: Sandipan Das <sandipan.das@xxxxxxx>
AuthorDate: Thu, 11 Aug 2022 18:00:01 +05:30
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Sat, 27 Aug 2022 00:05:45 +02:00
perf/x86/amd/lbr: Add LbrExtV2 branch speculation info support
Provide branch speculation information captured via AMD Last Branch Record
Extension Version 2 (LbrExtV2) by setting the speculation info in branch
records. The info is based on the "valid" and "spec" bits in the Branch To
registers.
Suggested-by: Stephane Eranian <eranian@xxxxxxxxxx>
Signed-off-by: Sandipan Das <sandipan.das@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/ddc02f6320464cad0e3ff5bdb2314531568a91bc.1660211399.git.sandipan.das@xxxxxxx
---
arch/x86/events/amd/lbr.c | 35 ++++++++++++++++++++++++++++++++---
1 file changed, 32 insertions(+), 3 deletions(-)
diff --git a/arch/x86/events/amd/lbr.c b/arch/x86/events/amd/lbr.c
index eb84f19..2e1c157 100644
--- a/arch/x86/events/amd/lbr.c
+++ b/arch/x86/events/amd/lbr.c
@@ -146,12 +146,19 @@ static void amd_pmu_lbr_filter(void)
}
}
+static const int lbr_spec_map[PERF_BR_SPEC_MAX] = {
+ PERF_BR_SPEC_NA,
+ PERF_BR_SPEC_WRONG_PATH,
+ PERF_BR_NON_SPEC_CORRECT_PATH,
+ PERF_BR_SPEC_CORRECT_PATH,
+};
+
void amd_pmu_lbr_read(void)
{
struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
struct perf_branch_entry *br = cpuc->lbr_entries;
struct branch_entry entry;
- int out = 0, i;
+ int out = 0, idx, i;
if (!cpuc->lbr_users)
return;
@@ -160,8 +167,11 @@ void amd_pmu_lbr_read(void)
entry.from.full = amd_pmu_lbr_get_from(i);
entry.to.full = amd_pmu_lbr_get_to(i);
- /* Check if a branch has been logged */
- if (!entry.to.split.valid)
+ /*
+ * Check if a branch has been logged; if valid = 0, spec = 0
+ * then no branch was recorded
+ */
+ if (!entry.to.split.valid && !entry.to.split.spec)
continue;
perf_clear_branch_entry_bitfields(br + out);
@@ -170,6 +180,25 @@ void amd_pmu_lbr_read(void)
br[out].to = sign_ext_branch_ip(entry.to.split.ip);
br[out].mispred = entry.from.split.mispredict;
br[out].predicted = !br[out].mispred;
+
+ /*
+ * Set branch speculation information using the status of
+ * the valid and spec bits.
+ *
+ * When valid = 0, spec = 0, no branch was recorded and the
+ * entry is discarded as seen above.
+ *
+ * When valid = 0, spec = 1, the recorded branch was
+ * speculative but took the wrong path.
+ *
+ * When valid = 1, spec = 0, the recorded branch was
+ * non-speculative but took the correct path.
+ *
+ * When valid = 1, spec = 1, the recorded branch was
+ * speculative and took the correct path
+ */
+ idx = (entry.to.split.valid << 1) | entry.to.split.spec;
+ br[out].spec = lbr_spec_map[idx];
out++;
}
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