From owner-freebsd-arm@FreeBSD.ORG Wed May 8 19:14:08 2013 Return-Path: Delivered-To: freebsd-arm@freebsd.org Received: from mx1.freebsd.org (mx1.FreeBSD.org [8.8.178.115]) by hub.freebsd.org (Postfix) with ESMTP id 6B699A9D; Wed, 8 May 2013 19:14:08 +0000 (UTC) (envelope-from adrian.chadd@gmail.com) Received: from mail-we0-x234.google.com (mail-we0-x234.google.com [IPv6:2a00:1450:400c:c03::234]) by mx1.freebsd.org (Postfix) with ESMTP id D2A40858; Wed, 8 May 2013 19:14:07 +0000 (UTC) Received: by mail-we0-f180.google.com with SMTP id n5so2057721wev.25 for ; Wed, 08 May 2013 12:14:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:x-received:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type; bh=YThnVooEQ//3KvjBsOMRkmrn2twsUVbnEyxDWuipX9U=; b=TVvRofvp2RyCGpuuNb+UGYr/ma5x0S7WAVPOq+WtY0HaU7TAEZLGNGIZjI+6UmJ9d1 bDa6BHF+/52MQQeQcpNfaWE1t56uE8Wg7+1Rdt3Me6KB94UO0uJNwpquCc2OQEFEbBnT tSTwcrkkpjmQw9YULQHcBkDzkCoAEF9IxvOxGL4HsjqfZ6kqiF0PxumqllgWsRaMUZNe QyV1WtS3NYqLcjXBEP4M/uF2vuyo3/+Zugy51Mo0RPvlarQ9XhueWmD4l0jtQrdB3qwY Pr5ISMiUUXNg7WHnK+PvSiIyRLMOopy/qSh5ywN33xdmbqjN0M+o2TtNR6BaQDJCTN5j qI5Q== MIME-Version: 1.0 X-Received: by 10.194.93.133 with SMTP id cu5mr12998122wjb.56.1368040446957; Wed, 08 May 2013 12:14:06 -0700 (PDT) Sender: adrian.chadd@gmail.com Received: by 10.217.58.138 with HTTP; Wed, 8 May 2013 12:14:06 -0700 (PDT) In-Reply-To: <1368025255.1180.200.camel@revolution.hippie.lan> References: <20130508085901.GA90732@server.rulingia.com> <20130508095414.GB90732@server.rulingia.com> <20130508104441.GC90732@server.rulingia.com> <1368025255.1180.200.camel@revolution.hippie.lan> Date: Wed, 8 May 2013 12:14:06 -0700 X-Google-Sender-Auth: 6YaFEfqOSMlxVkHPFlD0bcHqEM4 Message-ID: Subject: Re: Sawtooth ping RTT on RPi From: Adrian Chadd To: Ian Lepore Content-Type: text/plain; charset=ISO-8859-1 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 19:14:08 -0000 your other arm systems running -HEAD likely don't have USB ethernet.. :-) Adrian On 8 May 2013 08:00, Ian Lepore wrote: > 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 > >