From owner-freebsd-arch@FreeBSD.ORG Tue Feb 24 01:57:32 2015 Return-Path: Delivered-To: arch@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id E212EFA for ; Tue, 24 Feb 2015 01:57:32 +0000 (UTC) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 531E824E for ; Tue, 24 Feb 2015 01:57:32 +0000 (UTC) Received: from tom.home (kostik@localhost [127.0.0.1]) by kib.kiev.ua (8.14.9/8.14.9) with ESMTP id t1O1vMi9005887 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Tue, 24 Feb 2015 03:57:22 +0200 (EET) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.9.2 kib.kiev.ua t1O1vMi9005887 Received: (from kostik@localhost) by tom.home (8.14.9/8.14.9/Submit) id t1O1vMH3005886; Tue, 24 Feb 2015 03:57:22 +0200 (EET) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Tue, 24 Feb 2015 03:57:22 +0200 From: Konstantin Belousov To: John-Mark Gurney Subject: Re: locks and kernel randomness... Message-ID: <20150224015721.GT74514@kib.kiev.ua> References: <20150224012026.GY46794@funkthat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150224012026.GY46794@funkthat.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-Spam-Status: No, score=-2.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FREEMAIL_FROM,NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.0 X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on tom.home 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 01:57:33 -0000 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'. Please do not enforce yet another spinlock for the system.