Commit 0bc3be5b authored by Sandipan Das's avatar Sandipan Das Committed by Peter Zijlstra
Browse files

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: default avatarStephane Eranian <eranian@google.com>
Signed-off-by: default avatarSandipan Das <sandipan.das@amd.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/ddc02f6320464cad0e3ff5bdb2314531568a91bc.1660211399.git.sandipan.das@amd.com
parent 93315e46

arch/x86/events/amd/lbr.c

+32 −3
Original line number Diff line number Diff line
@@ -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++;

	}