netdev - Re: [PATCH net-next v5 2/2] selftests: fib_tests: Add a test case for IPv6 garbage collection

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Date: Thu, 3 Aug 2023 13:49:31 -0600
From: David Ahern <dsahern@...nel.org>
To: Kui-Feng Lee <sinquersw@...il.com>, thinker.li@...il.com,
 davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 netdev@...r.kernel.org, pabeni@...hat.com, martin.lau@...ux.dev,
 kernel-team@...a.com, yhs@...a.com
Cc: kuifeng@...a.com
Subject: Re: [PATCH net-next v5 2/2] selftests: fib_tests: Add a test case for
 IPv6 garbage collection

On 8/2/23 10:09 PM, Kui-Feng Lee wrote:
> 
> 
> On 8/2/23 19:06, David Ahern wrote:
>> On 8/1/23 6:43 PM, thinker.li@...il.com wrote:
>> \> @@ -747,6 +750,97 @@ fib_notify_test()
>>>       cleanup &> /dev/null
>>>   }
>>>   +fib6_gc_test()
>>> +{
>>> +    echo
>>> +    echo "Fib6 garbage collection test"
>>> +
>>> +    STRACE=$(which strace)
>>> +    if [ -z "$STRACE" ]; then
>>> +        echo "    SKIP: strace not found"
>>> +        ret=$ksft_skip
>>> +        return
>>> +    fi
>>> +
>>> +    EXPIRE=10
>>> +
>>> +    setup
>>> +
>>> +    set -e
>>> +
>>> +    # Check expiration of routes every 3 seconds (GC)
>>> +    $NS_EXEC sysctl -wq net.ipv6.route.gc_interval=300
>>> +
>>> +    $IP link add dummy_10 type dummy
>>> +    $IP link set dev dummy_10 up
>>> +    $IP -6 address add 2001:10::1/64 dev dummy_10
>>> +
>>> +    $NS_EXEC sysctl -wq net.ipv6.route.flush=1
>>> +
>>> +    # Temporary routes
>>> +    for i in $(seq 1 1000); do
>>> +        # Expire route after $EXPIRE seconds
>>> +        $IP -6 route add 2001:20::$i \
>>> +        via 2001:10::2 dev dummy_10 expires $EXPIRE
>>> +    done
>>> +    N_EXP=$($IP -6 route list |grep expires|wc -l)
>>> +    if [ $N_EXP -ne 1000 ]; then
>>
>> race condition here ... that you can install all 1000 routes and then
>> run this command before any expire. 10 seconds is normally more than
>> enough time, but on a loaded server it might not be. And really it does
>> not matter. What matters is that you install routes with an expires and
>> they disappear when expected - and I believe the flush below should not
>> be needed to validate they have been removed.
> 
> Without the flush below, the result will be very unpredictable or need
> to wait longer, at least two gc_interval seconds. We can
> shorten gc_interval to 10s, but we need to wait for 20s to make it
> certain. It is more predictable with the flush.
> 
> About race condition, I will remove the check.  Just like what you said,
> it is not necessary.

you do not need to measure how long it takes to remove expired routes in
a selftest; you are only testing that in fact the expired routes are
removed.

EXPIRES=1
install routes
# wait 2x expires time for removal
sleep 2
verify routes are removed.