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SubjectRe: [PATCH net-next] softirq: reduce latencies
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On Thu, 2013-01-03 at 11:41 -0800, Rick Jones wrote:

> In terms of netperf overhead, once you specify P99_LATENCY, you are
> already in for the pound of cost but only getting the penny of output
> (so to speak). While it would clutter the output, one could go ahead
> and ask for the other latency stats and it won't "cost" anything more:
>
> ... -- -k
> RT_LATENCY,MIN_LATENCY,MAX_LATENCY,P50_LATENCY,P90_LATENCY,P99_LATENCY,MEAN_LATENCY,STDDEV_LATENCY
>
> Additional information about how the omni output selectors work can be
> found at
> http://www.netperf.org/svn/netperf2/trunk/doc/netperf.html#Omni-Output-Selection
>
> happy benchmarking,
>
> rick jones
>
> BTW - you will likely see some differences between RT_LATENCY, which is
> calculated from the average transactions per second, and MEAN_LATENCY,
> which is calculated from the histogram of individual latencies
> maintained when any of the _LATENCY outputs other than RT_LATENCY is
> requested. Kudos to the folks at Google who did the extensions to the
> then-existing histogram code to enable it to be used for more reasonably
> accurate statistics.
>

Yeah ;)

Here are the before/after_patch results, cpu 2 handling the NIC irqs :


Before patch :

# netperf -H 7.7.7.84 -t TCP_RR -T2,2 -- -k
RT_LATENCY,MIN_LATENCY,MAX_LATENCY,P50_LATENCY,P90_LATENCY,P99_LATENCY,MEAN_LATENCY,STDDEV_LATENCY
MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET
to 7.7.7.84 () port 0 AF_INET : first burst 0 : cpu bind
RT_LATENCY=550110.424
MIN_LATENCY=146858
MAX_LATENCY=997109
P50_LATENCY=305000
P90_LATENCY=550000
P99_LATENCY=710000
MEAN_LATENCY=376989.12
STDDEV_LATENCY=184046.92

After patch :

# netperf -H 7.7.7.84 -t TCP_RR -T2,2 -- -k
RT_LATENCY,MIN_LATENCY,MAX_LATENCY,P50_LATENCY,P90_LATENCY,P99_LATENCY,MEAN_LATENCY,STDDEV_LATENCY
MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET
to 7.7.7.84 () port 0 AF_INET : first burst 0 : cpu bind
RT_LATENCY=40545.492
MIN_LATENCY=9834
MAX_LATENCY=78366
P50_LATENCY=33583
P90_LATENCY=59000
P99_LATENCY=69000
MEAN_LATENCY=38364.67
STDDEV_LATENCY=12865.26





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