Date: Tue, 10 Apr 2012 19:05:00 -0400 From: Barney Wolff <barney@databus.com> To: Julian Elischer <julian@freebsd.org> Cc: Luigi Rizzo <rizzo@iet.unipi.it>, current@freebsd.org, net@freebsd.org Subject: Re: strange ping response times... Message-ID: <20120410230500.GA22829@pit.databus.com> In-Reply-To: <4F84B6DB.5040904@freebsd.org> References: <20120410225257.GB53350@onelab2.iet.unipi.it> <4F84B6DB.5040904@freebsd.org>
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CPU cache? Cx states? powerd? On Tue, Apr 10, 2012 at 03:40:27PM -0700, Julian Elischer wrote: > 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..
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