Commit 93315e46 authored by Sandipan Das's avatar Sandipan Das Committed by Peter Zijlstra
Browse files

perf/core: Add speculation info to branch entries 



Add a new "spec" bitfield to branch entries for providing speculation
information. This will be populated using hints provided by branch sampling
features on supported hardware. The following cases are covered:

  * No branch speculation information is available
  * Branch is speculative but taken on the wrong path
  * Branch is non-speculative but taken on the correct path
  * Branch is speculative and taken on the correct path

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/834088c302faf21c7b665031dd111f424e509a64.1660211399.git.sandipan.das@amd.com
parent 245268c1

include/linux/perf_event.h

+1 −0
Original line number Diff line number Diff line
@@ -1078,6 +1078,7 @@ static inline void perf_clear_branch_entry_bitfields(struct perf_branch_entry *b 
	br->abort = 0;

	br->cycles = 0;

	br->type = 0;

	br->spec = PERF_BR_SPEC_NA;

	br->reserved = 0;

}

include/uapi/linux/perf_event.h

+14 −1
Original line number Diff line number Diff line
@@ -256,6 +256,17 @@ enum { 
	PERF_BR_MAX,

};



/*

 * Common branch speculation outcome classification

 */

enum {

	PERF_BR_SPEC_NA			= 0,	/* Not available */

	PERF_BR_SPEC_WRONG_PATH		= 1,	/* Speculative but on wrong path */

	PERF_BR_NON_SPEC_CORRECT_PATH	= 2,	/* Non-speculative but on correct path */

	PERF_BR_SPEC_CORRECT_PATH	= 3,	/* Speculative and on correct path */

	PERF_BR_SPEC_MAX,

};



#define PERF_SAMPLE_BRANCH_PLM_ALL \

	(PERF_SAMPLE_BRANCH_USER|\

	 PERF_SAMPLE_BRANCH_KERNEL|\
@@ -1363,6 +1374,7 @@ union perf_mem_data_src { 
 *     abort: aborting a hardware transaction

 *    cycles: cycles from last branch (or 0 if not supported)

 *      type: branch type

 *      spec: branch speculation info (or 0 if not supported)

 */

struct perf_branch_entry {

	__u64	from;
@@ -1373,7 +1385,8 @@ struct perf_branch_entry { 
		abort:1,    /* transaction abort */

		cycles:16,  /* cycle count to last branch */

		type:4,     /* branch type */

		reserved:40;

		spec:2,     /* branch speculation info */

		reserved:38;

};



union perf_sample_weight {