netdev - Re: Interpreting perf stat on netperf and netserver

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Message-ID: <CAL8zT=jP4Bm=WM0=OLcRgeetzXb0f_ZL0TiDvPAhkbA9UuxpBA@mail.gmail.com>
Date:	Thu, 19 Jan 2012 09:29:04 +0100
From:	Jean-Michel Hautbois <jhautbois@...il.com>
To:	Rick Jones <rick.jones2@...com>
Cc:	netdev@...r.kernel.org
Subject: Re: Interpreting perf stat on netperf and netserver

2012/1/18 Rick Jones <rick.jones2@...com>:
> On 01/18/2012 03:33 AM, Jean-Michel Hautbois wrote:
>>
>> Hi all,
>>
>> I am currently using netperf/netserver in order to characterize a
>> benet emulex network device on a machine with 2 Xeon5670.
>> I am using the latest linux kernel from git (3.2.0+).
>> I am facing several issues, and I am trying to understand the
>> following perf stat launched on netserver :
>>
>>  Performance counter stats for process id '5043':
>
>
> If you aren't already you may want to gather system-wide data as well - not
> everything networking is guaranteed to run in the netserver's (or netperf's)
> context.
>
> Might also be good to include the netperf command line driving that
> netserver.  That will help folks know if the netserver is receiving data
> (_STREAM), sending data (_MAERTS) or both (_RR) (though perhaps that can be
> gleaned from the routine names in the profile.

Well, I am only launching netserver without any parameter.

>
>>
>>       15452.992135 task-clock                #    0.450 CPUs utilized
>>             189678 context-switches          #    0.012 M/sec
>>                  5 CPU-migrations            #    0.000 M/sec
>>                275 page-faults               #    0.000 M/sec
>>        48490467936 cycles                    #    3.138 GHz
>>        33005879963 stalled-cycles-frontend   #   68.07% frontend cycles
>> idle
>>        16325855769 stalled-cycles-backend    #   33.67% backend  cycles
>> idle
>>        27340520316 instructions              #    0.56  insns per cycle
>>                                              #    1.21  stalled cycles per
>> insn
>>         4745604818 branches                  #  307.099 M/sec
>>           67513124 branch-misses             #    1.42% of all branches
>>
>>       34.303567279 seconds time elapsed
>>
>> I am trying to understand the "stalled-cycles-frontend" and
>> "stalled-cycles-backend" lines.
>> It seems that frontend is high, and in red :) but I can't say why...
>
>
> Perhaps the stalls are for cache misses - at least cache misses are a common
> reason for stalls.  I believe that perf has a way to be more specific about
> the PMU events of interest.

Yes, there is some events for that :). But I didn't know if stall was
cache misses related or not :).

JM
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