From owner-freebsd-arch@FreeBSD.ORG Wed Feb 25 10:21:25 2015 Return-Path: Delivered-To: freebsd-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 E0F22865 for ; Wed, 25 Feb 2015 10:21:25 +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 4E5DDD9B for ; Wed, 25 Feb 2015 10:21:25 +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 t1PALDjS047905 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Wed, 25 Feb 2015 12:21:13 +0200 (EET) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.9.2 kib.kiev.ua t1PALDjS047905 Received: (from kostik@localhost) by tom.home (8.14.9/8.14.9/Submit) id t1PALDno047904; Wed, 25 Feb 2015 12:21:13 +0200 (EET) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Wed, 25 Feb 2015 12:21:13 +0200 From: Konstantin Belousov To: Harrison Grundy Subject: Re: locks and kernel randomness... Message-ID: <20150225102113.GD74514@kib.kiev.ua> References: <20150224231921.GQ46794@funkthat.com> <1424822522.1328.11.camel@freebsd.org> <20150225002956.GT46794@funkthat.com> <2F49527F-2F58-4BD2-B8BE-1B1190CCD4D0@bsdimp.com> <54ED5656.50607@astrodoggroup.com> <20150225090638.GB74514@kib.kiev.ua> <54ED92E5.4010803@astrodoggroup.com> <54ED9A4B.4060802@astrodoggroup.com> <20150225100512.GC74514@kib.kiev.ua> <54EDA128.4000107@astrodoggroup.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54EDA128.4000107@astrodoggroup.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: freebsd-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: Wed, 25 Feb 2015 10:21:26 -0000 On Wed, Feb 25, 2015 at 02:17:12AM -0800, Harrison Grundy wrote: > > > On 02/25/15 02:05, Konstantin Belousov wrote: > > On Wed, Feb 25, 2015 at 01:47:55AM -0800, Harrison Grundy wrote: > >> Three choices here are attached here: > >> > >> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=197922 > >> > >> The only remaining one I don't have a patch for is putting a > >> "real" PRNG in ULE. > >> > >> At this point, as far as ULE goes, It just comes down to picking > >> from one of those approaches. > > > > The third patch, ' Creates sched_random, using the system used in > > cpu_search.', seems to miss updating the dpcpu randomval in > > sched_random(), isn't it ? > > > > It does exactly what cpu_search does. I do not see how it does exactly what cpu_search does. cpu_search is updating *rndptr: rnd = (*rndptr = *rndptr * 69069 + 5) >> 26; while code in patch is: + rndptr = DPCPU_PTR(randomval); + rnd = (*rndptr * 69069 + 5) >> 26; where is the write to *rndptr ? > > I really think the scheduler does not actually need randomness in > these locations. I've been running for the past few days on a few > systems here that way for testing purposes without issue. Why doing the arithmetic then ? > > I'll post a separate call for testers for a patch that overtly removes > them. ULE has a ton of different methods for balancing load between > cores (which is why you can turn off the long term balancer entirely).