cyclictest: Fix threads being affined even when -a isn't set

Using cyclictest without specifying affinity via -a, I was
noticing a strange issue where the rt threads where not
migrating when being blocked.

After lots of debugging in the kernel, I found its actually an
issue with cyclictest.

When using -t there is no behavioral difference between specifying
-a or not specifying -a.

This can be confirmed by adding printf messages around the
pthread_setaffinity_np() call in the threadtest function.

Currently:

root@localhost:~/rt-tests# ./cyclictest -t -a -q -D1
Affining thread 0 to cpu: 0
Affining thread 1 to cpu: 1
Affining thread 2 to cpu: 2
Affining thread 3 to cpu: 3
Affining thread 4 to cpu: 4
Affining thread 5 to cpu: 5
Affining thread 7 to cpu: 7
Affining thread 6 to cpu: 6
T: 0 (15034) P: 0 I:1000 C:   1000 Min:     82 Act:  184 Avg:  180 Max: 705
...

root@localhost:~/rt-tests# ./cyclictest -t -q -D1
Affining thread 0 to cpu: 0
Affining thread 1 to cpu: 1
Affining thread 2 to cpu: 2
Affining thread 3 to cpu: 3
Affining thread 4 to cpu: 4
Affining thread 5 to cpu: 5
Affining thread 6 to cpu: 6
Affining thread 7 to cpu: 7
T: 0 (15044) P: 0 I:1000 C:   1000 Min:     74 Act:  144 Avg:  162 Max: 860
..

This issue seems to come from the logic in process_options():
	/* if smp wasn't requested, test for numa automatically */
	if (!smp) {
		numa = numa_initialize();
		if (setaffinity == AFFINITY_UNSPECIFIED)
			setaffinity = AFFINITY_USEALL;
        }

Here, by setting setaffinity = AFFINITY_USEALL, we effectively
pin each thread to its respective cpu, same as the "-a" option.

This was most recently introduced in commit bdb8350f1b0b
("Revert "cyclictest: Use affinity_mask for steering
thread placement"").

This seems erronious to me, so I wanted to share this patch
which removes the overriding AFFINITY_UNSPECIFIED with
AFFINITY_USEALL by default. Also, some additional tweaks to
preserve the existing numa allocation affinity.

With this patch, we no longer call pthread_setaffinity_np() in the
"./cyclictest -t -q -D1"  case.

Cc: John Kacur <jkacur@redhat.com>
Cc: Connor O'Brien <connoro@google.com>
Cc: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: John Kacur <jkacur@redhat.com>

1 files changed, 6 insertions, 4 deletions

diff --git a/src/cyclictest/cyclictest.c b/src/cyclictest/cyclictest.c
index decea78..82759d1 100644
--- a/src/cyclictest/cyclictest.c
+++ b/src/cyclictest/cyclictest.c
@@ -1270,8 +1270,6 @@ static void process_options(int argc, char *argv[], int max_cpus)
 	/* if smp wasn't requested, test for numa automatically */
 	if (!smp) {
 		numa = numa_initialize();
-		if (setaffinity == AFFINITY_UNSPECIFIED)
-			setaffinity = AFFINITY_USEALL;
 	}
 
 	if (option_affinity) {
@@ -2043,9 +2041,13 @@ int main(int argc, char **argv)
 			void *stack;
 			void *currstk;
 			size_t stksize;
+			int node_cpu = cpu;
+
+			if (node_cpu == -1)
+				node_cpu = cpu_for_thread_ua(i, max_cpus);
 
 			/* find the memory node associated with the cpu i */
-			node = rt_numa_numa_node_of_cpu(cpu);
+			node = rt_numa_numa_node_of_cpu(node_cpu);
 
 			/* get the stack size set for this thread */
 			if (pthread_attr_getstack(&attr, &currstk, &stksize))
@@ -2056,7 +2058,7 @@ int main(int argc, char **argv)
 				stksize = PTHREAD_STACK_MIN * 2;
 
 			/*  allocate memory for a stack on appropriate node */
-			stack = rt_numa_numa_alloc_onnode(stksize, node, cpu);
+			stack = rt_numa_numa_alloc_onnode(stksize, node, node_cpu);
 
 			/* touch the stack pages to pre-fault them in */
 			memset(stack, 0, stksize);