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Date:   Wed, 5 Aug 2020 09:48:11 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Shuah Khan <shuah@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>, kernel-janitors@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] selftests/net: skip msg_zerocopy test if we have less
 than 4 CPUs

On 05/08/2020 09:44, Willem de Bruijn wrote:
> On Wed, Aug 5, 2020 at 10:22 AM Colin Ian King <colin.king@...onical.com> wrote:
>>
>> On 05/08/2020 09:06, Willem de Bruijn wrote:
>>> On Wed, Aug 5, 2020 at 2:54 AM Eric Dumazet <eric.dumazet@...il.com> wrote:
>>>>
>>>>
>>>>
>>>> On 8/4/20 5:30 AM, Colin King wrote:
>>>>> From: Colin Ian King <colin.king@...onical.com>
>>>>>
>>>>> 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 <colin.king@...onical.com>
>>>>> ---
>>>>>  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 :-)
> 
> Certainly not a bad fix! Thanks for addressing the issue. Alternative
> approach at
> 
> http://patchwork.ozlabs.org/project/netdev/patch/20200805084045.1549492-1-willemdebruijn.kernel@gmail.com/
> 
Thanks, you solution is good for my testing requirements

Acked-by: Colin Ian King <colin.king@...onical.com>

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