linux-kernel - Re: [PATCH net-next] softirq: reduce latencies

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Message-ID: <1357274510.21409.27807.camel@edumazet-glaptop>
Date:	Thu, 03 Jan 2013 20:41:50 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Rick Jones <rick.jones2@...com>
Cc:	sedat.dilek@...il.com, netdev@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] softirq: reduce latencies

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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