linux-kernel - Re: [LKP] [lkp] [sctp] a6c2f79287: netperf.Throughput

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Message-ID: <85b4c704-0598-bf18-92c5-edf04ab51597@intel.com>
Date:   Tue, 23 Aug 2016 17:19:54 +0800
From:   Aaron Lu <aaron.lu@...el.com>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:     Xin Long <lucien.xin@...il.com>,
        kernel test robot <xiaolong.ye@...el.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>, lkp@...org,
        "David S. Miller" <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.org>,
        "Chen, Tim C" <tim.c.chen@...el.com>,
        Huang Ying <ying.huang@...el.com>
Subject: Re: [LKP] [lkp] [sctp] a6c2f79287: netperf.Throughput_Mbps -37.2%
 regression

On 08/23/2016 05:44 AM, Marcelo Ricardo Leitner wrote:
> Em 19-08-2016 04:24, Aaron Lu escreveu:
>> On Fri, Aug 19, 2016 at 04:19:39AM -0300, Marcelo Ricardo Leitner wrote:
>>> Hi,
>>>
>>> Em 19-08-2016 02:29, Aaron Lu escreveu:
>>> ...
>>>> It doesn't look insane and sctp_wait_for_sndbuf may actually have
>>>> something to do with a larger sctp_chunk I suppose?
>>>>
>>>> The same perf record doesn't capture any sample for the good commit,
>>>> which suggests the nerperf process doesn't sleep in sctp_wait_for_sndbuf.
>>>
>>> Ahhh yes! It does, and then it would mean your txbuf is too small for the
>>> chunk sizes you're using (sctp tests option -m).
>>>
>>> What's your netperf cmdline again please?
>>
>> netperf -4 -t SCTP_STREAM_MANY -c -C -l 300 -- -m 10K -H 127.0.0.1
>>
>> Is the 10K used here a problem? If so, can you suggest a proper value
>> for our netperf performance test? Thanks.
> 
> We're still working on this. Xin could reproduce it on an i3 too, but 
> I'm afraid this commit just unmasked an issue in there. You're 
> overloading the CPU by too much when spawning 8 parallel netperf's on a 
> 4-core system, seems that commit a6c2f79287 was that last rock that made 
> it slip into a precipice. sctp's cwnd and rwnd management are not as 
> good as tcp's and now it seems you're triggering a corner case.

OK, I see.

> 
> I hope to have more soon.

Looking forward to test your patches.
Thanks for the update.

Regards,
Aaron