[PATCH net-next] selftests: net/forwarding: spawn sh inside vrf to speed up ping loop

[Jakub Kicinski <kuba@kernel.org>]

Looking at timestamped output of netdev CI reveals that
most of the time in forwarding tests for custom route
hashing is spent on a single case, namely the test which
uses ping (mausezahn does not support flow labels).

On a non-debug kernel we spend 714 of 730 total test
runtime (97%) on this test case. While having flow label
support in a traffic gen tool / mausezahn would be best,
we can significantly speed up the loop by putting ip vrf exec
outside of the iteration.

In a test of 1000 pings using a normal loop takes 50 seconds
to finish. While using:

  ip vrf exec $vrf sh -c "$loop-body"

takes 12 seconds (1/4 of the time).

Some of the slowness is likely due to our inefficient virtualization
setup, but even on my laptop running "ip link help" 16k times takes
25-30 seconds, so I think it's worth optimizing even for fastest
setups.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
CC: shuah@kernel.org
CC: idosch@nvidia.com
CC: linux-kselftest@vger.kernel.org
---
 .../selftests/net/forwarding/custom_multipath_hash.sh     | 8 ++++----
 .../selftests/net/forwarding/gre_custom_multipath_hash.sh | 8 ++++----
 .../net/forwarding/ip6gre_custom_multipath_hash.sh        | 8 ++++----
 3 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/tools/testing/selftests/net/forwarding/custom_multipath_hash.sh b/tools/testing/selftests/net/forwarding/custom_multipath_hash.sh
index 1783c10215e5..7d531f7091e6 100755
--- a/tools/testing/selftests/net/forwarding/custom_multipath_hash.sh
+++ b/tools/testing/selftests/net/forwarding/custom_multipath_hash.sh
@@ -224,10 +224,10 @@ send_dst_ipv6()
 send_flowlabel()
 {
 	# Generate 16384 echo requests, each with a random flow label.
-	for _ in $(seq 1 16384); do
-		ip vrf exec v$h1 \
-			$PING6 2001:db8:4::2 -F 0 -c 1 -q >/dev/null 2>&1
-	done
+	ip vrf exec v$h1 sh -c \
+		"for _ in {1..16384}; do \
+			$PING6 2001:db8:4::2 -F 0 -c 1 -q >/dev/null 2>&1; \
+		done"
 }
 
 send_src_udp6()
diff --git a/tools/testing/selftests/net/forwarding/gre_custom_multipath_hash.sh b/tools/testing/selftests/net/forwarding/gre_custom_multipath_hash.sh
index 9788bd0f6e8b..dda11a4a9450 100755
--- a/tools/testing/selftests/net/forwarding/gre_custom_multipath_hash.sh
+++ b/tools/testing/selftests/net/forwarding/gre_custom_multipath_hash.sh
@@ -319,10 +319,10 @@ send_dst_ipv6()
 send_flowlabel()
 {
 	# Generate 16384 echo requests, each with a random flow label.
-	for _ in $(seq 1 16384); do
-		ip vrf exec v$h1 \
-			$PING6 2001:db8:2::2 -F 0 -c 1 -q >/dev/null 2>&1
-	done
+	ip vrf exec v$h1 sh -c \
+		"for _ in {1..16384}; do \
+			$PING6 2001:db8:2::2 -F 0 -c 1 -q >/dev/null 2>&1; \
+		done"
 }
 
 send_src_udp6()
diff --git a/tools/testing/selftests/net/forwarding/ip6gre_custom_multipath_hash.sh b/tools/testing/selftests/net/forwarding/ip6gre_custom_multipath_hash.sh
index 2ab9eaaa5532..e28b4a079e52 100755
--- a/tools/testing/selftests/net/forwarding/ip6gre_custom_multipath_hash.sh
+++ b/tools/testing/selftests/net/forwarding/ip6gre_custom_multipath_hash.sh
@@ -321,10 +321,10 @@ send_dst_ipv6()
 send_flowlabel()
 {
 	# Generate 16384 echo requests, each with a random flow label.
-	for _ in $(seq 1 16384); do
-		ip vrf exec v$h1 \
-			$PING6 2001:db8:2::2 -F 0 -c 1 -q >/dev/null 2>&1
-	done
+	ip vrf exec v$h1 sh -c \
+		"for _ in {1..16384}; do \
+			$PING6 2001:db8:2::2 -F 0 -c 1 -q >/dev/null 2>&1; \
+		done"
 }
 
 send_src_udp6()
-- 
2.46.0