Date: Wed, 21 Jan 2015 11:32:39 -0800 From: Adrian Chadd <adrian@freebsd.org> To: Gleb Smirnoff <glebius@freebsd.org> Cc: Hans Petter Selasky <hps@selasky.org>, "src-committers@freebsd.org" <src-committers@freebsd.org>, "K. Macy" <kmacy@freebsd.org>, Jason Wolfe <nitroboost@gmail.com>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org>, Sean Bruno <sbruno@freebsd.org>, Konstantin Belousov <kostikbel@gmail.com> Subject: Re: svn commit: r277213 - in head: share/man/man9 sys/kern sys/ofed/include/linux sys/sys Message-ID: <CAJ-VmokyKX0uCA1%2B3KjziJkokDOVBCpUdwHQcVaY=buwa%2BqfhQ@mail.gmail.com> In-Reply-To: <20150121181512.GE15484@FreeBSD.org> References: <20150120075126.GA42409@kib.kiev.ua> <20150120211137.GY15484@FreeBSD.org> <54BED6FB.8060401@selasky.org> <54BEE62D.2060703@ignoranthack.me> <CAHM0Q_MDJN_8sTvTDXfqA7UtJVO3Y8S8%2BNRCs_=6Nj4dkTzjOA@mail.gmail.com> <54BEE8E6.3080009@ignoranthack.me> <CAHM0Q_N_53BM-6RvXu8UpjfDzQHEn5oXZo1Nn8RO0cuOUhe8tg@mail.gmail.com> <54BEEA7F.1070301@ignoranthack.me> <CAHM0Q_PtJ7JHFTiu9_dmi_Ce=rmu1j72z2OYQ2CD3%2BEbcoEGsA@mail.gmail.com> <54BEF154.3030606@ignoranthack.me> <20150121181512.GE15484@FreeBSD.org>
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On 21 January 2015 at 10:15, Gleb Smirnoff <glebius@freebsd.org> wrote: > Sean, > > On Tue, Jan 20, 2015 at 04:22:44PM -0800, Sean Bruno wrote: > S> In our universe, this commit (right or wrong) resolved our panics. I > S> think that there is some room for improvement based on the commentary > S> in this thread, but some people do indeed prefer stability over > S> performance. I hope we can come to a middle ground somewhere here. > > Sorry, but this sounds very much like alchemy. We poured this stuff > into that stuff and yield in gold precipitate. We don't understand > what's going on, but let's record the recipe into our tome of aclhemy > wisdom. > > So alchemy never came to a scientific level, and chemistry evolved > as science only when researchers started to measure, explain and > understand. > > If we treat our precious kernel in alchemy way, we will follow > the path of alchemy, except that it took centuries for alchemy to > die, and for a software product it would take a few years. > > So, for me Kip ideas sound very sensible. There could be a race > somewhere else. You tweak callout subsystem in any direction, > timings of events in kernel shift, your race is hidden. > > If we fix problems w/o understanding them, we are going alchemy way. Hi, I don't think it's quite this bad. They originally found that things were spinning for way too long. Hans found something similar and determined/concluded that the migration code in callouts was racy-by-design and dramatically simplified it and also put very hard constraints on what is a valid situation to support migrating from one callwheel to another. Now we have fallout which we can either address or back out until the callout stuff is again reviewed/fixed. I don't think it's as alchemic as is being promoted. -a
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