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Date:      Wed, 11 Apr 2012 00:09:48 -0400
From:      Jason Hellenthal <jhellenthal@dataix.net>
To:        Luigi Rizzo <rizzo@iet.unipi.it>
Cc:        current@freebsd.org, net@freebsd.org
Subject:   Re: strange ping response times...
Message-ID:  <20120411040948.GA24775@DataIX.net>
In-Reply-To: <20120410225257.GB53350@onelab2.iet.unipi.it>
References:  <20120410225257.GB53350@onelab2.iet.unipi.it>

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On Wed, Apr 11, 2012 at 12:52:57AM +0200, Luigi Rizzo wrote:
> I noticed this first on a 10G interface, but now there seems
> to be a similar issue on the loopback.
> 
> Apparently a ping -f has a much lower RTT than one with non-zero
> delay between transmissions. Part of the story could be that
> the flood version invokes a non-blocking select.
> On the other hand, pinging on the loopback should make
> the response available right away, so what could be the reason
> for the additional 3..10us in the ping response time ?
> 
> The following are numbers on an i7-2600k at 3400 MHz + turboboost,
> running stable/9 amd64. Note how the min ping time significantly
> increases moving from flood to 10ms to 1s.
> On an Intel 10G interface i am seeing a min of 14-16us with

Sorry but I am having trouble wrapping my head around this as the
results below are only for the loopback address 127.0.0.1 that does not
travel on the wire at all ? Did you assign this to the 10ge interface ?
if so which result is which. ?

In order to get any good results on my machine I had to tune the
following.

net.inet.icmp.reply_from_interface=1
net.inet.icmp.icmplim_output=0
net.inet.icmp.icmplim=0
net.inet.icmp.log_redirect=1

You may have other options if this is greater than stable/8 @ 234095

But yes the results seem skewed to some extent and being loopback I
would think there should be a very near zero rx/tx time.


> a ping flood, and up to 33-35us with the standard 1s interval
> (using -q probably trims another 2..5us)
> 
>     > sudo ping -c 1000 -q -f 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.002/0.003/0.012/0.001 ms
>     > sudo ping -c 1000 -q -f 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.002/0.002/0.013/0.001 ms
>     > sudo ping -c 1000 -q -f 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.002/0.002/0.013/0.001 ms
>     > sudo ping -c 10000 -q -f 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.002/0.002/0.011/0.001 ms
> 
>     > sudo ping -c 1000 -q -i 0.01 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.005/0.012/0.017/0.001 ms
>     > sudo ping -c 1000 -q -i 0.01 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.004/0.012/0.016/0.001 ms
>     > sudo ping -c 200 -q -i 0.01 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.007/0.012/0.017/0.002 ms
>     > sudo ping -c 200 -q -i 0.01 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.005/0.012/0.018/0.002 ms
>     > sudo ping -c 200 -q -i 0.01 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.009/0.012/0.020/0.002 ms
>     > sudo ping -c 200 -q -i 0.01 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.006/0.012/0.016/0.001 ms
> 
>     > sudo ping -c 200 -q -i 0.1 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.007/0.014/0.020/0.001 ms
>     > sudo ping -c 200 -q -i 0.1 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.006/0.014/0.019/0.002 ms
>     > sudo ping -c 200 -q -i 0.1 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.007/0.014/0.021/0.001 ms
>     > sudo ping -c 200 -q -i 0.1 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.007/0.014/0.020/0.001 ms
>     > sudo ping -c 200 -q -i 0.1 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.006/0.014/0.021/0.002 ms
>     > sudo ping -c 200 -q -i 0.1 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.010/0.014/0.022/0.001 ms
> 
>     > sudo ping -c 20 -q -i 1  127.0.0.1
> 	round-trip min/avg/max/stddev = 0.013/0.018/0.022/0.002 ms
>     > sudo ping -c 20 -q -i 1 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.012/0.018/0.021/0.002 ms
>     > sudo ping -c 20 -q -i 1 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.009/0.017/0.018/0.002 ms
>     > sudo ping -c 20 -q -i 1 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.011/0.017/0.021/0.002 ms
>     > sudo ping -c 20 -q -i 1 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.010/0.017/0.020/0.002 ms
>     > sudo ping -c 20 -q -i 1 127.0.0.1
> 	round-trip min/avg/max/stddev = 0.009/0.017/0.028/0.004 ms
> 
> cheers
> luigi
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-- 
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