Date: Wed, 25 Feb 2015 12:21:13 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Harrison Grundy <harrison.grundy@astrodoggroup.com> Cc: freebsd-arch@freebsd.org Subject: Re: locks and kernel randomness... Message-ID: <20150225102113.GD74514@kib.kiev.ua> In-Reply-To: <54EDA128.4000107@astrodoggroup.com> 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>
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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).
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