[Gluster-devel] Problems with ec/nfs.t in regression tests

Thu Feb 12 18:04:39 UTC 2015

On 02/12/2015 08:15 PM, Xavier Hernandez wrote:
> I've made some more investigation and the problem seems worse.
>
> It seems that NFS sends a huge amount of requests without waiting for 
> answers (I've had more than 1400 requests ongoing). Probably there 
> will be many factors that can influence on the load that this causes, 
> and one of them could be ec, but it's not related exclusively to ec. 
> I've repeated the test using a replica 3 and a replica 2 volumes and 
> the problem still happens.
>
> The test basically writes a file to an NFS mount using 'dd'. The file 
> has a size of 1GB. With a smaller file, the test passes successfully.
Using NFS client and gluster NFS server on same machine with BIG file dd 
operations is known to cause hangs. anon-fd-quota.t used to give similar 
problems so we changed the test to not involve NFS mounts.

Pranith
>
> One important thing to note is that I'm not using powerful servers (a 
> dual core Intel Atom), but this problem shouldn't happen anyway. It 
> can even happen on more powerful servers if they are busy doing other 
> things (maybe this is what's happening on jenkins' slaves).
>
> I think that this causes some NFS requests to timeout. This can be 
> seen in /var/log/messages (there are many of these messages):
>
> Feb 12 15:18:45 celler01 kernel: nfs: server gf01.datalab.es not 
> responding, timed out
>
> nfs log also has many errors:
>
> [2015-02-12 14:18:45.132905] E [rpcsvc.c:1257:rpcsvc_submit_generic] 
> 0-rpc-service: failed to submit message (XID: 0x7be78dbe, Program: 
> NFS3, ProgVers: 3, Proc: 7) to rpc
> -transport (socket.nfs-server)
> [2015-02-12 14:18:45.133009] E [nfs3.c:565:nfs3svc_submit_reply] 
> 0-nfs-nfsv3: Reply submission failed
>
> Additionally this causes disconnections from NFS that are not 
> correctly handled causing that a thread gets stuck in an infinite loop 
> (I haven't analyzed this problem deeply, but it seems like an attempt 
> to use an already disconnected socket). After a while, I get this 
> error on the nfs log:
>
> [2015-02-12 14:20:19.545429] C 
> [rpc-clnt-ping.c:109:rpc_clnt_ping_timer_expired] 0-patchy-client-0: 
> server 192.168.200.61:49152 has not responded in the last 42 seconds, 
> disconnecting.
>
> The console executing the test shows this (nfs.t is creating a replica 
> 3 instead of a dispersed volume):
>
> # ./run-tests.sh tests/basic/ec/nfs.t
>
> ... GlusterFS Test Framework ...
>
> Running tests in file ./tests/basic/ec/nfs.t
> [14:12:52] ./tests/basic/ec/nfs.t .. 8/10 dd: error writing 
> ‘/mnt/nfs/0/test’: Input/output error
> [14:12:52] ./tests/basic/ec/nfs.t .. 9/10
> not ok 9
> [14:12:52] ./tests/basic/ec/nfs.t .. Failed 1/10 subtests
> [14:27:41]
>
> Test Summary Report
> -------------------
> ./tests/basic/ec/nfs.t (Wstat: 0 Tests: 10 Failed: 1)
>   Failed test:  9
> Files=1, Tests=10, 889 wallclock secs ( 0.13 usr  0.02 sys +  1.29 
> cusr  3.45 csys =  4.89 CPU)
> Result: FAIL
> Failed tests  ./tests/basic/ec/nfs.t
>
> Note that the test takes almost 15 minutes to complete.
>
> Is there any way to limit the number of requests NFS sends without 
> having an answer ?
>
> Xavi
>
> On 02/11/2015 04:20 PM, Shyam wrote:
>> On 02/11/2015 09:40 AM, Xavier Hernandez wrote:
>>> Hi,
>>>
>>> it seems that there are some failures in ec/nfs.t test on regression
>>> tests. Doing some investigation I've found that before applying the
>>> multi-threaded patch (commit 5e25569e) the problem does not seem to
>>> happen.
>>
>> This has in interesting history in failures, on the regression runs for
>> the MT epoll this (i.e ec/nfs.t) did not fail (there were others, but
>> not nfs.t).
>>
>> The patch that allows configuration of MT epoll is where this started
>> failing around Feb 5th (but later passed). (see patchset 7 failures on,
>> http://review.gluster.org/#/c/9488/ )
>>
>> I state the above, as it may help narrowing down the changes in EC
>> (maybe) that could have caused it.
>>
>> Also in the latter commit, there was an error configuring the number of
>> threads so all regression runs would have run with a single epoll thread
>> (the MT epoll patch had this hard coded, so that would have run with 2
>> threads, but did not show up the issue (patch:
>> http://review.gluster.org/#/c/3842/)).
>>
>> Again I state the above, as this should not be exposing a
>> race/bug/problem due to the multi threaded nature of epoll, but of
>> course needs investigation.
>>
>>>
>>> I'm not sure if this patch is the cause or it has revealed some bug in
>>> ec or any other xlator.
>>
>> I guess we can reproduce this issue? If so I would try setting
>> client.event-threads on master branch to 1, restarting the volume and
>> then running the test (as a part of the test itself maybe) to eliminate
>> the possibility that MT epoll is causing it.
>>
>> My belief on MT epoll causing it is in doubt as the runs failed on the
>> http://review.gluster.org/#/c/9488/ (configuration patch), which had the
>> thread count as 1 due to a bug in that code.
>>
>>>
>>> I can try to identify it (any help will be appreciated), but it may 
>>> take
>>> some time. Would it be better to remove the test in the meantime ?
>>
>> I am checking if this is reproducible on my machine, so that I can
>> possibly see what is going wrong.
>>
>> Shyam
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