netdev - Re: [PATCH net] selftests: net: wait for receiver startup in so

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Date: Fri, 09 Feb 2024 17:45:28 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Willem de Bruijn <willemb@...gle.com>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>,  Jakub Kicinski <kuba@...nel.org>, Shuah Khan
 <shuah@...nel.org>, Vinicius Costa Gomes <vinicius.gomes@...el.com>,
 linux-kselftest@...r.kernel.org,  netdev@...r.kernel.org
Subject: Re: [PATCH net] selftests: net: wait for receiver startup in
 so_txtime.sh

On Fri, 2024-02-09 at 15:51 +0100, Paolo Abeni wrote:
> On Thu, 2024-02-08 at 16:45 +0100, Paolo Abeni wrote:
> > The mentioned test is failing in slow environments:
> > 
> >   # SO_TXTIME ipv4 clock monotonic
> >   # ./so_txtime: recv: timeout: Resource temporarily unavailable
> >   not ok 1 selftests: net: so_txtime.sh # exit=1
> > 
> > The receiver is started in background and the sender could end-up
> > transmitting the packet before the receiver is ready, so that the
> > later recv times out.
> > 
> > Address the issue explcitly waiting for the socket being bound to
> > the relevant port.
> > 
> > Fixes: af5136f95045 ("selftests/net: SO_TXTIME with ETF and FQ")
> > Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> > ---
> > Note that to really cope with slow env the mentioned self-tests also
> > need net-next commit c41dfb0dfbec ("selftests/net: ignore timing
> > errors in so_txtime if KSFT_MACHINE_SLOW"), so this could be applied to
> > net-next, too
> 
> Oops... CI is saying the above is not enough...
> 
> > @@ -65,6 +70,7 @@ do_test() {
> >  
> >  	local readonly START="$(date +%s%N --date="+ 0.1 seconds")"
> >  	ip netns exec "${NS2}" "${BIN}" -"${IP}" -c "${CLOCK}" -t "${START}" -S "${SADDR}" -D "${DADDR}" "${RXARGS}" -r &
> > +	wait_local_port_listen "${NS2}" 8000 "${PROTO}"
> >  	ip netns exec "${NS1}" "${BIN}" -"${IP}" -c "${CLOCK}" -t "${START}" -S "${SADDR}" -D "${DADDR}" "${TXARGS}"
> 
> The binary explicitly waits up to $START time, and that conflicts with
> the wait_local_port_listen, something different is needed. Apparently I
> was just "lucky" during my local testing.

I experimented a few different solutions and so far the only option
that gave some positive result is increasing start delay and the etf
delta by an order of magnitude, see below.

But I'm pretty sure that even with that there will be sporadic failures
in slow enough environments.

When the host-induced jitter/delay is high enough, packets are dropped
and there are functional failures. I'm wondering if we should skip this
test entirely when KSFT_MACHINE_SLOW=yes.

Do you see any other options?

Paolo

---
diff --git a/tools/testing/selftests/net/so_txtime.sh b/tools/testing/selftests/net/so_txtime.sh
index 3f06f4d286a9..6445580f0a66 100755
--- a/tools/testing/selftests/net/so_txtime.sh
+++ b/tools/testing/selftests/net/so_txtime.sh
@@ -63,7 +63,9 @@ do_test() {
 		exit 1
 	fi
 
-	local readonly START="$(date +%s%N --date="+ 0.1 seconds")"
+	local delta=0.1
+	[ -n "${KSFT_MACHINE_SLOW}" ] && delta=1
+	local readonly START="$(date +%s%N --date="+ ${delta} seconds")"
 	ip netns exec "${NS2}" "${BIN}" -"${IP}" -c "${CLOCK}" -t "${START}" -S "${SADDR}" -D "${DADDR}" "${RXARGS}" -r &
 	ip netns exec "${NS1}" "${BIN}" -"${IP}" -c "${CLOCK}" -t "${START}" -S "${SADDR}" -D "${DADDR}" "${TXARGS}"
 	wait "$!"
@@ -76,7 +78,9 @@ do_test 6 mono a,10 a,10
 do_test 4 mono a,10,b,20 a,10,b,20
 do_test 6 mono a,20,b,10 b,20,a,20
 
-if ip netns exec "${NS1}" tc qdisc replace dev "${DEV}" root etf clockid CLOCK_TAI delta 400000; then
+delta=400000
+[ -n "${KSFT_MACHINE_SLOW}" ] && delta=$((delta*10))
+if ip netns exec "${NS1}" tc qdisc replace dev "${DEV}" root etf clockid CLOCK_TAI delta "${delta}"; then
 	! do_test 4 tai a,-1 a,-1
 	! do_test 6 tai a,0 a,0
 	do_test 6 tai a,10 a,10