Re: strange ping response times...

From: Julian Elischer <julian_at_freebsd.org>
Date: Tue, 10 Apr 2012 15:40:27 -0700
On 4/10/12 3:52 PM, 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
> a ping flood, and up to 33-35us with the standard 1s interval
> (using -q probably trims another 2..5us)

I'd suggest some ktr points around the loopback path..

>      >  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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Received on Tue Apr 10 2012 - 20:39:46 UTC

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