netdev - Re: [PATCH bpf v3 3/5] selftests/bpf: test

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Date:   Thu, 31 May 2018 13:13:57 +0900
From:   Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>
To:     John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S . Miller" <davem@...emloft.net>,
        Shuah Khan <shuah@...nel.org>, netdev@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf v3 3/5] selftests/bpf: test_sockmap, fix test timeout



On 5/31/2018 4:59 AM, John Fastabend wrote:
> On 05/30/2018 12:29 PM, Alexei Starovoitov wrote:
>> On Wed, May 30, 2018 at 02:56:09PM +0900, Prashant Bhole wrote:
>>> In order to reduce runtime of tests, recently timout for select() call
>>> was reduced from 1sec to 10usec. This was causing many tests failures.
>>> It was caught with failure handling commits in this series.
>>>
>>> Restoring the timeout from 10usec to 1sec
>>>
>>> Fixes: a18fda1a62c3 ("bpf: reduce runtime of test_sockmap tests")
>>> Signed-off-by: Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>
>>> ---
>>>   tools/testing/selftests/bpf/test_sockmap.c | 4 ++--
>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/tools/testing/selftests/bpf/test_sockmap.c b/tools/testing/selftests/bpf/test_sockmap.c
>>> index 64f9e25c451f..9d01f5c2abe2 100644
>>> --- a/tools/testing/selftests/bpf/test_sockmap.c
>>> +++ b/tools/testing/selftests/bpf/test_sockmap.c
>>> @@ -345,8 +345,8 @@ static int msg_loop(int fd, int iov_count, int iov_length, int cnt,
>>>   		if (err < 0)
>>>   			perror("recv start time: ");
>>>   		while (s->bytes_recvd < total_bytes) {
>>> -			timeout.tv_sec = 0;
>>> -			timeout.tv_usec = 10;
>>> +			timeout.tv_sec = 1;
>>> +			timeout.tv_usec = 0;
>>
>> I've applied the set, but had to revert it, since it takes too long.
>>
>> real	1m40.124s
>> user	0m0.375s
>> sys	0m14.521s
>>
> 
> Dang, I thought it would be a bit longer but not minutes.
> 
>> Myself and Daniel run the test semi-manually when we apply patches.> Adding 2 extra minutes of wait time is unnecessary.
> 
> Yep.
> 
>> Especially since most of it is idle time.
>> Please find a way to fix tests differently.
>> btw I don't see any failures today. Not sure what is being fixed
>> by incresing a timeout.
>>
> 
> Calling these fixes is a bit much, they are primarily improvements.
> 
> The background is, when I originally wrote the tests my goal was to
> exercise the kernel code paths. Because of this I didn't really care if
> the tests actually sent/recv all bytes in the test. (I have long
> running tests using netperf/wrk/apached/etc. for that) But, the manual
> tests do have an option to verify the data if specified. The 'verify'
> option is a bit fragile in that with the right tests (e.g. drop)
> or the certain options (e.g. cork) it can fail which is expected.
> 
> What Prashant added was support to actually verify the data correctly.
> And also fix a few cgroup handling and some pretty printing as well.
> He noticed the low timeout causing issue in these cases though so
> increased it.
> 
> @Prashant, how about increasing this less dramatically because now
> all cork tests are going to stall for 1s unless perfectly aligned.
> How about 100us? Or even better we can conditionally set it based
> on if tx_cork is set. If tx_cork is set use 1us otherwise use 200us
> or something. (1s is really to high in any cases for lo)
> 
> Also capturing some of the above in the cover letter would help
> folks understand the context a bit better.
> 

I did trial and error for timeout values. Currently 1000us for corked 
tests and 1 sec for other tests works fine. I observed broken-pipe error 
at tx side when timeout was < 1000us.

Also tests with apply=1 and higher number of iterations were taking 
time, so reducing iterations reduces the test run time drastically.

real    0m12.968s
user    0m0.219s
sys     0m14.337s

Also I will try to explain background in the cover letter of next series.

-Prashant