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perf/x86/amd/lbr: Add LbrExtV2 branch speculation info support

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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@google.com>
Signed-off-by: Sandipan Das <sandipan.das@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/ddc02f6320464cad0e3ff5bdb2314531568a91bc.1660211399.git.sandipan.das@amd.com
This commit is contained in:
Sandipan Das 2022-08-11 18:00:01 +05:30 committed by Peter Zijlstra
parent 93315e46b0
commit 0bc3be5b4b
1 changed files with 32 additions and 3 deletions
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35
arch/x86/events/amd/lbr.c
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@ -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++;
}