From owner-freebsd-current@FreeBSD.ORG Mon Nov 21 16:49:42 2011 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 5B0F1106564A; Mon, 21 Nov 2011 16:49:42 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from cyrus.watson.org (cyrus.watson.org [65.122.17.42]) by mx1.freebsd.org (Postfix) with ESMTP id 31A1B8FC1A; Mon, 21 Nov 2011 16:49:42 +0000 (UTC) Received: from bigwig.baldwin.cx (96.47.65.170.static.nyinternet.net [96.47.65.170]) by cyrus.watson.org (Postfix) with ESMTPSA id DD67446B46; Mon, 21 Nov 2011 11:49:41 -0500 (EST) Received: from jhbbsd.localnet (unknown [209.249.190.124]) by bigwig.baldwin.cx (Postfix) with ESMTPSA id AD6B3B978; Mon, 21 Nov 2011 11:49:38 -0500 (EST) From: John Baldwin To: Luigi Rizzo Date: Mon, 21 Nov 2011 11:29:29 -0500 User-Agent: KMail/1.13.5 (FreeBSD/8.2-CBSD-20110714-p8; KDE/4.5.5; amd64; ; ) References: <4EC6AEF0.1010402@FreeBSD.org> <20111118220458.GA21152@onelab2.iet.unipi.it> In-Reply-To: <20111118220458.GA21152@onelab2.iet.unipi.it> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201111211129.29362.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.7 (bigwig.baldwin.cx); Mon, 21 Nov 2011 11:49:38 -0500 (EST) Cc: Matteo Landi , Doug Barton , freebsd-current@freebsd.org Subject: Re: ixgbe and fast interrupts X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 21 Nov 2011 16:49:42 -0000 On Friday, November 18, 2011 5:04:58 pm Luigi Rizzo wrote: > On Fri, Nov 18, 2011 at 11:16:00AM -0800, Doug Barton wrote: > > On 11/18/2011 09:54, Luigi Rizzo wrote: > > > One more thing (i am mentioning it here for archival purposes, > > > as i keep forgetting to test it). Is entropy harvesting expensive ? > > > > No. It was designed to be inexpensive on purpose. :) > > hmmm.... > unfortunately I don't have a chance to test it until monday > (probably one could see if the ping times change by modifying > the value of kern.random.sys.harvest.* ). > > But in the code i see the following: > > - the harvest routine is this: > > void > random_harvest(void *entropy, u_int count, u_int bits, u_int frac, > enum esource origin) > { > if (reap_func) > (*reap_func)(get_cyclecount(), entropy, count, bits, frac, > origin); > } > > - the reap_func seems to be bound to > > dev/random/randomdev_soft.c::random_harvest_internal() > > which internally uses a spinlock and then moves entries between > two lists. > > I am concerned that the get_cyclecount() might end up querying an > expensive device (is it using kern.timecounter.hardware ?) On modern x86 it just does rdtsc(). > So between the indirect function call, spinlock, list manipulation > and the cyclecounter i wouldn't be surprised it the whole thing > takes a microsecond or so. I suspect it is not quite that expensive. > Anyways, on monday i'll know better. in the meantime, if someone > wants to give it a try... in our tests between two machines and > ixgbe (10G) interfaces, an unmodified 9.0 kernel has a median ping > time of 30us with "slow" pings (say -i 0.01 or larger) and 17us with > a ping -f . Did you time it with harvest.interrupt disabled? -- John Baldwin