[PATCH v5 08/11] alpha/perf: report the ProfileMe window count as the sample weight

[Matt Turner <mattst88@gmail.com>]

What PCTR1 counted during the ProfileMe window, the inum retire delay for
cycles:p or the window length for instructions:p, is only available in
the PERF_SAMPLE_RAW data.

Report it in var1_dw of the sample weight, which the weight and
local_weight sort keys read. It is 20 bits, so it fits. As Alpha is
little-endian, this is also the right value for plain PERF_SAMPLE_WEIGHT,
which is what perf record -W asks for. Samples that fall back to the
interrupted PC get no weight, as it belongs to a different instruction.

Suggested-by: Ian Rogers <irogers@google.com>
Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Matt Turner <mattst88@gmail.com>
---
 arch/alpha/kernel/perf_event.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/alpha/kernel/perf_event.c b/arch/alpha/kernel/perf_event.c
index 6c74f67ad341..c2c367b51617 100644
--- a/arch/alpha/kernel/perf_event.c
+++ b/arch/alpha/kernel/perf_event.c
@@ -1030,7 +1030,7 @@ static void alpha_perf_event_profileme(struct perf_event *event,
 	struct perf_raw_record raw;
 	struct perf_sample_data data;
 	struct pt_regs *pm_regs;
-	bool pc_only = false;
+	bool pc_only = false, exact = true;
 	unsigned long pctr_ctl, i_stat, pmpc, ovr, pc, saved_pc, saved_ps;
 
 	pctr_ctl = wrperfmon(PERFMON_CMD_READ, 0);
@@ -1077,6 +1077,7 @@ static void alpha_perf_event_profileme(struct perf_event *event,
 	pc = pmpc & EV67_PMPC_PC_MASK;
 	if (pmpc & EV67_PMPC_PAL) {
 		pc = regs->pc;
+		exact = false;
 	} else if (pc < TASK_SIZE && !user_mode(regs)) {
 		if (is_user_task(current)) {
 			pc_only = true;
@@ -1086,6 +1087,7 @@ static void alpha_perf_event_profileme(struct perf_event *event,
 			pm_regs->ps = 8;
 		} else {
 			pc = regs->pc;
+			exact = false;
 		}
 	} else if (pc >= TASK_SIZE && user_mode(regs)) {
 		pm_regs = this_cpu_ptr(&alpha_profileme_regs);
@@ -1119,6 +1121,15 @@ static void alpha_perf_event_profileme(struct perf_event *event,
 	};
 	perf_sample_save_raw_data(&data, event, &raw);
 
+	/* The count belongs to the profiled instruction, not the interrupted PC. */
+	if (exact && (event->attr.sample_type & PERF_SAMPLE_WEIGHT_TYPE)) {
+		/* perf_sample_data_init() does not clear it. */
+		data.weight.full = 0;
+		data.weight.var1_dw = (pctr_ctl >> EV67_PCTR_1_COUNT_SHIFT) &
+				      EV67_PCTR_1_COUNT_MASK;
+		data.sample_flags |= PERF_SAMPLE_WEIGHT_TYPE;
+	}
+
 	if (!alpha_perf_event_set_period(event, hwc, 0))
 		return;
 

-- 
2.55.0