selftests/powerpc: Add a test of counting larx/stcx

This is based on the count_instructions test.

However this one also counts the number of failed stcx's, and in
conjunction with knowing the size of the stcx loop, can calculate the
total number of instructions executed even in the face of
non-deterministic stcx failures.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200426114410.3917383-1-mpe@ellerman.id.au

tools/testing/selftests/powerpc/pmu/.gitignore

@@ -2,3 +2,4 @@
 count_instructions
 l3_bank_test
 per_event_excludes
+count_stcx_fail

tools/testing/selftests/powerpc/pmu/Makefile

@@ -2,7 +2,7 @@
 noarg:
 	$(MAKE) -C ../
 
-TEST_GEN_PROGS := count_instructions l3_bank_test per_event_excludes
+TEST_GEN_PROGS := count_instructions count_stcx_fail l3_bank_test per_event_excludes
 EXTRA_SOURCES := ../harness.c event.c lib.c ../utils.c
 
 top_srcdir = ../../../../..
@@ -13,8 +13,12 @@ all: $(TEST_GEN_PROGS) ebb
 $(TEST_GEN_PROGS): $(EXTRA_SOURCES)
 
 # loop.S can only be built 64-bit
+$(OUTPUT)/count_instructions: CFLAGS += -m64
 $(OUTPUT)/count_instructions: loop.S count_instructions.c $(EXTRA_SOURCES)
-	$(CC) $(CFLAGS) -m64 -o $@ $^
+
+$(OUTPUT)/count_stcx_fail: CFLAGS += -m64
+$(OUTPUT)/count_stcx_fail: loop.S $(EXTRA_SOURCES)
+
 
 $(OUTPUT)/per_event_excludes: ../utils.c
 

tools/testing/selftests/powerpc/pmu/count_stcx_fail.c

+/*
+ * Copyright 2013, Michael Ellerman, IBM Corp.
+ * Licensed under GPLv2.
+ */
+
+#define _GNU_SOURCE
+
+#include <stdio.h>
+#include <stdbool.h>
+#include <string.h>
+#include <sys/prctl.h>
+
+#include "event.h"
+#include "utils.h"
+#include "lib.h"
+
+extern void thirty_two_instruction_loop_with_ll_sc(u64 loops, u64 *ll_sc_target);
+
+static void setup_event(struct event *e, u64 config, int type, char *name)
+{
+	event_init_opts(e, config, type, name);
+
+	e->attr.disabled = 1;
+	e->attr.exclude_kernel = 1;
+	e->attr.exclude_hv = 1;
+	e->attr.exclude_idle = 1;
+}
+
+static int do_count_loop(struct event *events, u64 instructions,
+			 u64 overhead, bool report)
+{
+	s64 difference, expected;
+	double percentage;
+	u64 dummy;
+
+	prctl(PR_TASK_PERF_EVENTS_ENABLE);
+
+	/* Run for 1M instructions */
+	thirty_two_instruction_loop_with_ll_sc(instructions >> 5, &dummy);
+
+	prctl(PR_TASK_PERF_EVENTS_DISABLE);
+
+	event_read(&events[0]);
+	event_read(&events[1]);
+	event_read(&events[2]);
+
+	expected = instructions + overhead + (events[2].result.value * 10);
+	difference = events[0].result.value - expected;
+	percentage = (double)difference / events[0].result.value * 100;
+
+	if (report) {
+		printf("-----\n");
+		event_report(&events[0]);
+		event_report(&events[1]);
+		event_report(&events[2]);
+
+		printf("Looped for %llu instructions, overhead %llu\n", instructions, overhead);
+		printf("Expected %llu\n", expected);
+		printf("Actual   %llu\n", events[0].result.value);
+		printf("Delta    %lld, %f%%\n", difference, percentage);
+	}
+
+	event_reset(&events[0]);
+	event_reset(&events[1]);
+	event_reset(&events[2]);
+
+	if (difference < 0)
+		difference = -difference;
+
+	/* Tolerate a difference below 0.0001 % */
+	difference *= 10000 * 100;
+	if (difference / events[0].result.value)
+		return -1;
+
+	return 0;
+}
+
+/* Count how many instructions it takes to do a null loop */
+static u64 determine_overhead(struct event *events)
+{
+	u64 current, overhead;
+	int i;
+
+	do_count_loop(events, 0, 0, false);
+	overhead = events[0].result.value;
+
+	for (i = 0; i < 100; i++) {
+		do_count_loop(events, 0, 0, false);
+		current = events[0].result.value;
+		if (current < overhead) {
+			printf("Replacing overhead %llu with %llu\n", overhead, current);
+			overhead = current;
+		}
+	}
+
+	return overhead;
+}
+
+#define	PM_MRK_STCX_FAIL	0x03e158
+#define PM_STCX_FAIL	0x01e058
+
+static int test_body(void)
+{
+	struct event events[3];
+	u64 overhead;
+
+	setup_event(&events[0], PERF_COUNT_HW_INSTRUCTIONS, PERF_TYPE_HARDWARE, "instructions");
+	setup_event(&events[1], PERF_COUNT_HW_CPU_CYCLES, PERF_TYPE_HARDWARE, "cycles");
+	setup_event(&events[2], PM_STCX_FAIL, PERF_TYPE_RAW, "stcx_fail");
+
+	if (event_open(&events[0])) {
+		perror("perf_event_open");
+		return -1;
+	}
+
+	if (event_open_with_group(&events[1], events[0].fd)) {
+		perror("perf_event_open");
+		return -1;
+	}
+
+	if (event_open_with_group(&events[2], events[0].fd)) {
+		perror("perf_event_open");
+		return -1;
+	}
+
+	overhead = determine_overhead(events);
+	printf("Overhead of null loop: %llu instructions\n", overhead);
+
+	/* Run for 1Mi instructions */
+	FAIL_IF(do_count_loop(events, 1000000, overhead, true));
+
+	/* Run for 10Mi instructions */
+	FAIL_IF(do_count_loop(events, 10000000, overhead, true));
+
+	/* Run for 100Mi instructions */
+	FAIL_IF(do_count_loop(events, 100000000, overhead, true));
+
+	/* Run for 1Bi instructions */
+	FAIL_IF(do_count_loop(events, 1000000000, overhead, true));
+
+	/* Run for 16Bi instructions */
+	FAIL_IF(do_count_loop(events, 16000000000, overhead, true));
+
+	/* Run for 64Bi instructions */
+	FAIL_IF(do_count_loop(events, 64000000000, overhead, true));
+
+	event_close(&events[0]);
+	event_close(&events[1]);
+
+	return 0;
+}
+
+static int count_ll_sc(void)
+{
+	return eat_cpu(test_body);
+}
+
+int main(void)
+{
+	return test_harness(count_ll_sc, "count_ll_sc");
+}

tools/testing/selftests/powerpc/pmu/loop.S

@@ -41,3 +41,38 @@ FUNC_START(thirty_two_instruction_loop)
 	subi	r3,r3,1
 	b	FUNC_NAME(thirty_two_instruction_loop)
 FUNC_END(thirty_two_instruction_loop)
+
+FUNC_START(thirty_two_instruction_loop_with_ll_sc)
+	cmpdi	r3,0
+	beqlr
+	addi	r5,r5,1
+	addi	r5,r5,1
+	addi	r5,r5,1		# 5
+	addi	r5,r5,1
+	addi	r5,r5,1
+	addi	r5,r5,1
+	addi	r5,r5,1
+1:	ldarx	r6,0,r4		# 10
+	addi	r5,r5,1
+	addi	r5,r5,1
+	addi	r5,r5,1
+	addi	r5,r5,1
+	addi	r5,r5,1		# 15
+	addi	r5,r5,1
+	addi	r5,r5,1
+	stdcx.	r6,0,r4
+	bne-	1b
+	addi	r5,r5,1		# 20
+	addi	r5,r5,1
+	addi	r5,r5,1
+	addi	r5,r5,1
+	addi	r5,r5,1
+	addi	r5,r5,1		# 25
+	addi	r5,r5,1
+	addi	r5,r5,1
+	addi	r5,r5,1
+	addi	r5,r5,1
+	addi	r5,r5,1		# 30
+	subi	r3,r3,1
+	b	FUNC_NAME(thirty_two_instruction_loop_with_ll_sc)
+FUNC_END(thirty_two_instruction_loop_with_ll_sc)