Re: [PATCH] selftests/net: skip msg_zerocopy test if we have less than 4 CPUs

On 05/08/2020 09:06, Willem de Bruijn wrote:

On Wed, Aug 5, 2020 at 2:54 AM Eric Dumazet [off-list ref] wrote:

quoted

On 8/4/20 5:30 AM, Colin King wrote:

quoted

From: Colin Ian King <redacted>

The current test will exit with a failure if it cannot set affinity on
specific CPUs which is problematic when running this on single CPU
systems. Add a check for the number of CPUs and skip the test if
the CPU requirement is not met.

Signed-off-by: Colin Ian King <redacted>
---
 tools/testing/selftests/net/msg_zerocopy.sh | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tools/testing/selftests/net/msg_zerocopy.sh b/tools/testing/selftests/net/msg_zerocopy.sh
index 825ffec85cea..97bc527e1297 100755
--- a/tools/testing/selftests/net/msg_zerocopy.sh
+++ b/tools/testing/selftests/net/msg_zerocopy.sh

@@ -21,6 +21,11 @@ readonly DADDR6='fd::2'

 readonly path_sysctl_mem="net.core.optmem_max"

+if [[ $(nproc) -lt 4 ]]; then
+     echo "SKIP: test requires at least 4 CPUs"
+     exit 4
+fi
+
 # No arguments: automated test
 if [[ "$#" -eq "0" ]]; then
      $0 4 tcp -t 1

Test explicitly uses CPU 2 and 3, right ?

nproc could be 500, yet cpu 2 or 3 could be offline

# cat /sys/devices/system/cpu/cpu3/online
0
# echo $(nproc)
71

The cpu affinity is only set to bring some stability across runs.

The test does not actually verify that a run with zerocopy is some
factor faster than without, as that factor is hard to choose across
all platforms. As a result the automated run mainly gives code coverage.

It's preferable to always run. And on sched_setaffinity failure log a
message about possible jitter and continue. I can send that patch, if
the approach sounds good.

That's sounds preferable to my bad fix for sure :-)

Colin