[PATCH net-next 2/5] selftests: mlxsw: sch_red_core: Increase backlog size tolerance

[Petr Machata <petrm@nvidia.com>]

Backlog fluctuates on Spectrum-4 much more than on <4. In practice we can
sample queue depth values going from about -12% to about +7% of the
configured RED limit. The test which checks the queue size has a limit of
+-10%, and as a result often fails. We attempted to fix the issue by
busywaiting for several seconds hoping to get within the bounds, but that
still proved to be too noisy (or the wait time would be impractically
long). Unfortunately we have to bump the value tolerance from 10% to 15%,
which in this patch do.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Amit Cohen <amcohen@nvidia.com>
---
 tools/testing/selftests/drivers/net/mlxsw/sch_red_core.sh | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/drivers/net/mlxsw/sch_red_core.sh b/tools/testing/selftests/drivers/net/mlxsw/sch_red_core.sh
index 299e06a5808c..a25a15eb6d31 100644
--- a/tools/testing/selftests/drivers/net/mlxsw/sch_red_core.sh
+++ b/tools/testing/selftests/drivers/net/mlxsw/sch_red_core.sh
@@ -532,10 +532,11 @@ do_red_test()
 	check_fail $? "Traffic went into backlog instead of being early-dropped"
 	pct=$(check_marking get_nmarked $vlan "== 0")
 	check_err $? "backlog $backlog / $limit Got $pct% marked packets, expected == 0."
+	backlog=$(get_qdisc_backlog $vlan)
 	local diff=$((limit - backlog))
 	pct=$((100 * diff / limit))
-	((-10 <= pct && pct <= 10))
-	check_err $? "backlog $backlog / $limit expected <= 10% distance"
+	((-15 <= pct && pct <= 15))
+	check_err $? "backlog $backlog / $limit expected <= 15% distance"
 	log_test "TC $((vlan - 10)): RED backlog > limit"
 
 	stop_traffic
-- 
2.45.0