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.
With this patch, we no longer call pthread_setaffinity_np() in the
"./cyclictest -t -q -D1" case.
Cc: John Kacur <jkacur@xxxxxxxxxx>
Cc: Connor O'Brien <connoro@xxxxxxxxxx>
Cc: Qais Yousef <qais.yousef@xxxxxxx>
Signed-off-by: John Stultz <jstultz@xxxxxxxxxx>
---
src/cyclictest/cyclictest.c | 2 --
1 file changed, 2 deletions(-)
diff --git a/src/cyclictest/cyclictest.c b/src/cyclictest/cyclictest.c
index decea78..02f32f6 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) {
--
2.37.1.359.gd136c6c3e2-goog
