From owner-freebsd-arch@FreeBSD.ORG Mon Mar 2 17:10:27 2015 Return-Path: Delivered-To: arch@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id AE82D97D; Mon, 2 Mar 2015 17:10:27 +0000 (UTC) Received: from gold.funkthat.com (gate2.funkthat.com [208.87.223.18]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "gold.funkthat.com", Issuer "gold.funkthat.com" (not verified)) by mx1.freebsd.org (Postfix) with ESMTPS id 16E8734D; Mon, 2 Mar 2015 17:10:27 +0000 (UTC) Received: from gold.funkthat.com (localhost [127.0.0.1]) by gold.funkthat.com (8.14.5/8.14.5) with ESMTP id t22HAQSW049882 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 2 Mar 2015 09:10:26 -0800 (PST) (envelope-from jmg@gold.funkthat.com) Received: (from jmg@localhost) by gold.funkthat.com (8.14.5/8.14.5/Submit) id t22HAQ3k049881; Mon, 2 Mar 2015 09:10:26 -0800 (PST) (envelope-from jmg) Date: Mon, 2 Mar 2015 09:10:26 -0800 From: John-Mark Gurney To: Alfred Perlstein Subject: Re: locks and kernel randomness... Message-ID: <20150302171025.GO32329@funkthat.com> References: <20150224012026.GY46794@funkthat.com> <1824482166.23183751.1425303073196.JavaMail.zimbra@stormshield.eu> <54F47C98.2080505@freebsd.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54F47C98.2080505@freebsd.org> X-Operating-System: FreeBSD 9.1-PRERELEASE amd64 X-PGP-Fingerprint: 54BA 873B 6515 3F10 9E88 9322 9CB1 8F74 6D3F A396 X-Files: The truth is out there X-URL: http://resnet.uoregon.edu/~gurney_j/ X-Resume: http://resnet.uoregon.edu/~gurney_j/resume.html X-TipJar: bitcoin:13Qmb6AeTgQecazTWph4XasEsP7nGRbAPE X-to-the-FBI-CIA-and-NSA: HI! HOW YA DOIN? can i haz chizburger? User-Agent: Mutt/1.5.21 (2010-09-15) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.7 (gold.funkthat.com [127.0.0.1]); Mon, 02 Mar 2015 09:10:26 -0800 (PST) Cc: Emeric POUPON , arch@freebsd.org X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 02 Mar 2015 17:10:27 -0000 Alfred Perlstein wrote this message on Mon, Mar 02, 2015 at 10:07 -0500: > On 3/2/15 8:31 AM, Emeric POUPON wrote: > > About arc4random, we have noticed significant contention in that function on multi CPU systems when ciphering a lot of packets in the IPsec stack. > > This is indeed due to the mutex that is being used in the arc4rand function. > > > > Actually randomness is required by the IV used in the forged output packets. > > However, making a separate random generator per CPU might be more complicated than expected. > > The RFC 6027 (http://www.ietf.org/rfc/rfc6027.txt) reminds that the IV must not be repeated : > > --- > > 3.7.1. Outbound SAs Using Counter Modes > > > > For SAs involving counter mode ciphers such as Counter Mode (CTR) > > ([RFC3686]) or Galois/Counter Mode (GCM) ([RFC4106]) there is yet > > another complication. The initial vector for such modes MUST NOT be > > repeated, and senders use methods such as counters or linear feedback > > shift registers (LFSRs) to ensure this [...] > > --- > > > > What do you think? > > If you can not have multiple random sources then what do you think of > having a thread that pre-fetches batches of random values and queues it > to each cpu? If you have the queue be pretty large then you shouldn't > bottleneck on it. > > Sort of like UMA for random data. > > Sorry if this is a daft idea, not sure about this code path in general, > but this struck me as a potential workaround. I'd say that's needlessly complex... You'd still need a lock, or play w/ the scheduler (sched_bind) to serialize access to the PCPU random pool... -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."