From owner-freebsd-arm@FreeBSD.ORG Wed May 8 15:01:01 2013 Return-Path: Delivered-To: freebsd-arm@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by hub.freebsd.org (Postfix) with ESMTP id 0BB404EF; Wed, 8 May 2013 15:01:00 +0000 (UTC) (envelope-from ian@FreeBSD.org) Received: from mho-01-ewr.mailhop.org (mho-03-ewr.mailhop.org [204.13.248.66]) by mx1.freebsd.org (Postfix) with ESMTP id 86DDB5ED; Wed, 8 May 2013 15:01:00 +0000 (UTC) Received: from c-24-8-230-52.hsd1.co.comcast.net ([24.8.230.52] helo=damnhippie.dyndns.org) by mho-01-ewr.mailhop.org with esmtpsa (TLSv1:AES256-SHA:256) (Exim 4.72) (envelope-from ) id 1Ua5rX-000MWt-GF; Wed, 08 May 2013 15:00:59 +0000 Received: from [172.22.42.240] (revolution.hippie.lan [172.22.42.240]) by damnhippie.dyndns.org (8.14.3/8.14.3) with ESMTP id r48F0tlx016921; Wed, 8 May 2013 09:00:56 -0600 (MDT) (envelope-from ian@FreeBSD.org) X-Mail-Handler: Dyn Standard SMTP by Dyn X-Originating-IP: 24.8.230.52 X-Report-Abuse-To: abuse@dyndns.com (see http://www.dyndns.com/services/sendlabs/outbound_abuse.html for abuse reporting information) X-MHO-User: U2FsdGVkX1/u8sx0FZGFAuAEipDoKF/W Subject: Re: Sawtooth ping RTT on RPi From: Ian Lepore To: Peter Jeremy In-Reply-To: <20130508104441.GC90732@server.rulingia.com> References: <20130508085901.GA90732@server.rulingia.com> <20130508095414.GB90732@server.rulingia.com> <20130508104441.GC90732@server.rulingia.com> Content-Type: text/plain; charset="us-ascii" Date: Wed, 08 May 2013 09:00:55 -0600 Message-ID: <1368025255.1180.200.camel@revolution.hippie.lan> Mime-Version: 1.0 X-Mailer: Evolution 2.32.1 FreeBSD GNOME Team Port Content-Transfer-Encoding: 7bit Cc: freebsd-arm@FreeBSD.org X-BeenThere: freebsd-arm@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Porting FreeBSD to the StrongARM Processor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 08 May 2013 15:01:01 -0000 On Wed, 2013-05-08 at 20:44 +1000, Peter Jeremy wrote: > On 2013-May-08 03:12:43 -0700, Adrian Chadd wrote: > >yup, that looks like two almost-but-not-in-sync sampling periods (one > >being poll, one being ping) beating against each other. > > That seems like a reasonable hypothesis. > > >Is the USB stuff being polled? > > I'm not sure. I don't think so. dmesg says: > > dwcotg0: mem 0x20980000-0x2099ffff irq 17 on simplebus0 > usbus0 on dwcotg0 > smsc0: on usbus0 > ue0: on smsc0 > > So there's an interrupt available and nothing else is using irq 17. > And systat shows that the interrupt rate on irq 17 goes up with > network traffic (though it idles at ~500 interrupts/sec - which seems > excessive). > Just to make all of this even more confusing, my RPi results always look like this with kern.hz set to one of 100, 500, 1000, 2500: PING revolution.hippie.lan (172.22.42.240): 56 data bytes 64 bytes from 172.22.42.240: icmp_seq=0 ttl=64 time=7.739 ms 64 bytes from 172.22.42.240: icmp_seq=1 ttl=64 time=10.130 ms 64 bytes from 172.22.42.240: icmp_seq=2 ttl=64 time=10.115 ms 64 bytes from 172.22.42.240: icmp_seq=3 ttl=64 time=10.146 ms However, with kern.hz=250, I get this: PING revolution.hippie.lan (172.22.42.240): 56 data bytes 64 bytes from 172.22.42.240: icmp_seq=0 ttl=64 time=5.839 ms 64 bytes from 172.22.42.240: icmp_seq=1 ttl=64 time=8.169 ms 64 bytes from 172.22.42.240: icmp_seq=2 ttl=64 time=8.156 ms 64 bytes from 172.22.42.240: icmp_seq=3 ttl=64 time=8.145 ms And with kern.hz=333, it looks like this: PING revolution.hippie.lan (172.22.42.240): 56 data bytes 64 bytes from 172.22.42.240: icmp_seq=0 ttl=64 time=6.757 ms 64 bytes from 172.22.42.240: icmp_seq=1 ttl=64 time=9.126 ms 64 bytes from 172.22.42.240: icmp_seq=2 ttl=64 time=9.208 ms 64 bytes from 172.22.42.240: icmp_seq=3 ttl=64 time=9.252 ms Very strange. No matter what kern.hz is set to, I always get a shorter time on the first packet, and then after that the variance from one packet to the next is always within about 100us. My other arm systems running -current don't behave like this. -- Ian