Subject: [PATCH 2/4] tools/perf: Fix perf bench epoll to correct usage of affinity for machines with #CPUs > 1K

From: Athira Rajeev <[email-masked]>
Date: Sat, 2 Apr 2022 00:28:51 +0530

perf bench epoll testcase fails on systems with CPU's
more than 1K.

Testcase: perf bench epoll all
Result snippet:
<<>>
Run summary [PID 106497]: 1399 threads monitoring on 64 file-descriptors for 8 secs.

perf: pthread_create: No such file or directory
<<>>

In epoll benchmarks (ctl, wait) pthread_create is invoked in do_threads
from respective bench_epoll_*  function. Though the logs shows direct
failure from pthread_create, the actual failure is from  "sched_setaffinity"
returning EINVAL (invalid argument). This happens because the default
mask size in glibc is 1024. To overcome this 1024 CPUs mask size
limitation of cpu_set_t, change the mask size using the CPU_*_S macros.

Patch addresses this by fixing all the epoll benchmarks to use
CPU_ALLOC to allocate cpumask, CPU_ALLOC_SIZE for size, and
CPU_SET_S to set the mask.

Reported-by: Disha Goel <[email-masked]>
Signed-off-by: Athira Rajeev <[email-masked]>
---
 tools/perf/bench/epoll-ctl.c  | 25 +++++++++++++++++++------
 tools/perf/bench/epoll-wait.c | 25 +++++++++++++++++++------
 2 files changed, 38 insertions(+), 12 deletions(-)

diff --git a/tools/perf/bench/epoll-ctl.c b/tools/perf/bench/epoll-ctl.c
index 1a17ec83d3c4..91c53f6c6d87 100644
--- a/tools/perf/bench/epoll-ctl.c
+++ b/tools/perf/bench/epoll-ctl.c
@@ -222,13 +222,20 @@ static void init_fdmaps(struct worker *w, int pct)
 static int do_threads(struct worker *worker, struct perf_cpu_map *cpu)
 {
 	pthread_attr_t thread_attr, *attrp = NULL;
-	cpu_set_t cpuset;
+	cpu_set_t *cpuset;
 	unsigned int i, j;
 	int ret = 0;
+	int nrcpus;
+	size_t size;
 
 	if (!noaffinity)
 		pthread_attr_init(&thread_attr);
 
+	nrcpus = perf_cpu_map__nr(cpu);
+	cpuset = CPU_ALLOC(nrcpus);
+	BUG_ON(!cpuset);
+	size = CPU_ALLOC_SIZE(nrcpus);
+
 	for (i = 0; i < nthreads; i++) {
 		struct worker *w = &worker[i];
 
@@ -252,22 +259,28 @@ static int do_threads(struct worker *worker, struct perf_cpu_map *cpu)
 			init_fdmaps(w, 50);
 
 		if (!noaffinity) {
-			CPU_ZERO(&cpuset);
-			CPU_SET(perf_cpu_map__cpu(cpu, i % perf_cpu_map__nr(cpu)).cpu, &cpuset);
+			CPU_ZERO_S(size, cpuset);
+			CPU_SET_S(perf_cpu_map__cpu(cpu, i % perf_cpu_map__nr(cpu)).cpu,
+					size, cpuset);
 
-			ret = pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpuset);
-			if (ret)
+			ret = pthread_attr_setaffinity_np(&thread_attr, size, cpuset);
+			if (ret) {
+				CPU_FREE(cpuset);
 				err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
+			}
 
 			attrp = &thread_attr;
 		}
 
 		ret = pthread_create(&w->thread, attrp, workerfn,
 				     (void *)(struct worker *) w);
-		if (ret)
+		if (ret) {
+			CPU_FREE(cpuset);
 			err(EXIT_FAILURE, "pthread_create");
+		}
 	}
 
+	CPU_FREE(cpuset);
 	if (!noaffinity)
 		pthread_attr_destroy(&thread_attr);
 
diff --git a/tools/perf/bench/epoll-wait.c b/tools/perf/bench/epoll-wait.c
index 0d1dd8879197..9469a53ffab9 100644
--- a/tools/perf/bench/epoll-wait.c
+++ b/tools/perf/bench/epoll-wait.c
@@ -291,9 +291,11 @@ static void print_summary(void)
 static int do_threads(struct worker *worker, struct perf_cpu_map *cpu)
 {
 	pthread_attr_t thread_attr, *attrp = NULL;
-	cpu_set_t cpuset;
+	cpu_set_t *cpuset;
 	unsigned int i, j;
 	int ret = 0, events = EPOLLIN;
+	int nrcpus;
+	size_t size;
 
 	if (oneshot)
 		events |= EPOLLONESHOT;
@@ -306,6 +308,11 @@ static int do_threads(struct worker *worker, struct perf_cpu_map *cpu)
 	if (!noaffinity)
 		pthread_attr_init(&thread_attr);
 
+	nrcpus = perf_cpu_map__nr(cpu);
+	cpuset = CPU_ALLOC(nrcpus);
+	BUG_ON(!cpuset);
+	size = CPU_ALLOC_SIZE(nrcpus);
+
 	for (i = 0; i < nthreads; i++) {
 		struct worker *w = &worker[i];
 
@@ -341,22 +348,28 @@ static int do_threads(struct worker *worker, struct perf_cpu_map *cpu)
 		}
 
 		if (!noaffinity) {
-			CPU_ZERO(&cpuset);
-			CPU_SET(perf_cpu_map__cpu(cpu, i % perf_cpu_map__nr(cpu)).cpu, &cpuset);
+			CPU_ZERO_S(size, cpuset);
+			CPU_SET_S(perf_cpu_map__cpu(cpu, i % perf_cpu_map__nr(cpu)).cpu,
+					size, cpuset);
 
-			ret = pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpuset);
-			if (ret)
+			ret = pthread_attr_setaffinity_np(&thread_attr, size, cpuset);
+			if (ret) {
+				CPU_FREE(cpuset);
 				err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
+			}
 
 			attrp = &thread_attr;
 		}
 
 		ret = pthread_create(&w->thread, attrp, workerfn,
 				     (void *)(struct worker *) w);
-		if (ret)
+		if (ret) {
+			CPU_FREE(cpuset);
 			err(EXIT_FAILURE, "pthread_create");
+		}
 	}
 
+	CPU_FREE(cpuset);
 	if (!noaffinity)
 		pthread_attr_destroy(&thread_attr);
 
-- 
2.35.1