Date: Wed, 11 Apr 2012 12:35:10 +0200 From: Andre Oppermann <andre@freebsd.org> To: Luigi Rizzo <rizzo@iet.unipi.it> Cc: Barney Wolff <barney@databus.com>, current@freebsd.org, net@freebsd.org Subject: Re: strange ping response times... Message-ID: <4F855E5E.5000107@freebsd.org> In-Reply-To: <20120410233211.GA53829@onelab2.iet.unipi.it> References: <20120410225257.GB53350@onelab2.iet.unipi.it> <4F84B6DB.5040904@freebsd.org> <20120410230500.GA22829@pit.databus.com> <20120410233211.GA53829@onelab2.iet.unipi.it>
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On 11.04.2012 01:32, Luigi Rizzo wrote: > On Tue, Apr 10, 2012 at 07:05:00PM -0400, Barney Wolff wrote: >> CPU cache? >> Cx states? >> powerd? > > powerd is disabled, and i am going down to C1 at most > > sysctl -a | grep cx > hw.acpi.cpu.cx_lowest: C1 > dev.cpu.0.cx_supported: C1/1 C2/80 C3/104 > > which shouldn't take so much. Sure, cache matters, but the > fact is, icmp processing on loopback should occur inline. > > unless there is a forced descheduling on a select with timeout> 0 > which would explain the extra few microseconds (and makes me worry > on how expensive is a scheduling decision...) Things going through loopback go through a NETISR and may end up queued to avoid LOR situations. In addition per-cpu queues with hash-distribution for affinity may cause your packet to be processed by a different core. Hence the additional delay. -- Andre
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