[netperf-talk] Negative number of message Okay in UDP_STREAM Test

[Rick Jones]

On 12/06/2012 10:40 PM, Piyush Verma wrote:
> Here I found the output of UDP_STREAM test for 24 hrs and getting
> negative number of message Okay packets-
>
> [root at rhel61-srv-64 vermap]# ./netperf -H 172.16.128.155 -p 49152 -t
> udp_stream -l 86400 -- -m 8192 -s 32768 -S 65536   &
> [1] 4115
>   UDP UNIDIRECTIONAL SEND TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to
> 172.16.128.155 (172.16.128.155) port 0 AF_INET
>
> Socket  Message  Elapsed      Messages
> Size    Size     Time         Okay Errors   Throughput
> bytes   bytes    secs            #      #   10^6bits/sec
>
>   65536    8192   86400.00   -2081184671      0    1679.20
> 131072           86400.00   -2081420383           1679.02
>
> Please let me know what does negative message Okay means here?

It means that the likely 32 bit signed value being used to count message 
has "wrapped."  That is, in that 24 hour period netperf sent over ~2 
billion messages.

Given that I don't see "MIGRATED" in the test banner, I'm guessing the 
(unstated) netperf version is earlier than 2.5.0.  If having a negative 
value there is a problem, you might give top-of-trunk a try, where the 
counters for the number of send calls have been bumped to 64 bit. 
However, looking at the definition for what is returned by the netserver 
side, that one can still wrap around - it is an unsigned 32-bit quantity.

Netperf wasn't really ever expected to have a single instance run that 
long. Typically 24 hours for a benchmark is considered a tad excessive. 
  Of course, some folks (ab)use netperf for functional QA purposes - 24 
CHO  and such.  In that case, if negative values are an issue, and 24 
hours of operation  under one netperf command line is still required, I 
might suggest (ab)using the confidence intervals.  Set the width quite 
wide and the confidence low, and then make the number of iterations the 
maximum - 30 - with the run time 86400/30 or 2880:

netperf -H 172.16.128.155 -p 49152 -t udp_stream -I 95,50 -i 30,30 -l 
2880 -m 8192 -s 32768 -S 65536

Or, just run a series of shorter-length netperfs in a row.

happy benchmarking,

rick jones