From owner-freebsd-arch@FreeBSD.ORG Tue Feb 24 02:09:03 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 BC4E75EE for ; Tue, 24 Feb 2015 02:09:03 +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 7CDD8392 for ; Tue, 24 Feb 2015 02:09:03 +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 t1O292WQ096909 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 23 Feb 2015 18:09:02 -0800 (PST) (envelope-from jmg@gold.funkthat.com) Received: (from jmg@localhost) by gold.funkthat.com (8.14.5/8.14.5/Submit) id t1O292nB096908; Mon, 23 Feb 2015 18:09:02 -0800 (PST) (envelope-from jmg) Date: Mon, 23 Feb 2015 18:09:02 -0800 From: John-Mark Gurney To: Konstantin Belousov Subject: Re: locks and kernel randomness... Message-ID: <20150224020902.GZ46794@funkthat.com> References: <20150224012026.GY46794@funkthat.com> <20150224015721.GT74514@kib.kiev.ua> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150224015721.GT74514@kib.kiev.ua> 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, 23 Feb 2015 18:09:02 -0800 (PST) Cc: 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: Tue, 24 Feb 2015 02:09:03 -0000 Konstantin Belousov wrote this message on Tue, Feb 24, 2015 at 03:57 +0200: > On Mon, Feb 23, 2015 at 05:20:26PM -0800, John-Mark Gurney wrote: > > I'm working on simplifying kernel randomness interfaces. I would like > > to get read of all weak random generators, and this means replacing > > read_random and random(9) w/ effectively arc4rand(9) (to be replaced > > by ChaCha or Keccak in the future). > > > > The issue is that random(9) is called from any number of contexts, such > > as the scheduler. This makes locking a bit more interesting. Currently, > > both arc4rand(9) and yarrow/fortuna use a default mtx lock to protect > > their state. This obviously isn't compatible w/ the scheduler, and > > possibly other calling contexts. > > > > I have a patch[1] that unifies the random interface. It converts a few > > of the locks from mtx default to mtx spin to deal w/ this. > This is definitely an overkill. The rebalancing minor use of randomness > absolutely does not require cryptographical-strenght randomness to > select a moment to rebalance thread queue. Imposing the spin lock on > the whole random machinery just to allow the same random gathering code > to be used for balance_ticks is detriment to the system responsivness. > Scheduler is fine even with congruential generators, as you could see in > the cpu_search(), look for the '69069'. Then why doesn't it use this then? This is exactly why I don't want random to be a congruential generator... If you're so sure that you don't need cryptographic secure and that it's a performance benefit to do so, then you're free to roll your own, but almost all of the time, code won't meet both requirements. I haven't audited all the places where random is currently being called that might require not sleeping. The scheduler happens to be the first one I ran into... > Please do not enforce yet another spinlock for the system. I sent this email asking for help for how to avoid a spin lock. I'd appreciate if you could suggest how to improve my patch. Thanks. -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."