From owner-freebsd-hackers@freebsd.org Sat Mar 2 10:57:02 2019 Return-Path: Delivered-To: freebsd-hackers@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 4F20A151D4C1; Sat, 2 Mar 2019 10:57:02 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 714D488D03; Sat, 2 Mar 2019 10:57:01 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kib@localhost [127.0.0.1]) by kib.kiev.ua (8.15.2/8.15.2) with ESMTPS id x22AurQx005364 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Sat, 2 Mar 2019 12:56:56 +0200 (EET) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua x22AurQx005364 Received: (from kostik@localhost) by tom.home (8.15.2/8.15.2/Submit) id x22AuqMq005363; Sat, 2 Mar 2019 12:56:52 +0200 (EET) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Sat, 2 Mar 2019 12:56:52 +0200 From: Konstantin Belousov To: Ian Lepore Cc: Poul-Henning Kamp , Mark Millard , Mark Millard via freebsd-hackers , Konstantin Belousov , bde@freebsd.org, FreeBSD PowerPC ML Subject: Re: powerpc64 head -r344018 stuck sleeping problems: th->th_scale * tc_delta(th) overflows unsigned 64 bits sometimes [patched failed] Message-ID: <20190302105652.GD68879@kib.kiev.ua> References: <20190228145542.GT2420@kib.kiev.ua> <20190228150811.GU2420@kib.kiev.ua> <962D78C3-65BE-40C1-BB50-A0088223C17B@yahoo.com> <28C2BB0A-3DAA-4D18-A317-49A8DD52778F@yahoo.com> <20190301112717.GW2420@kib.kiev.ua> <679402FF-907C-43AF-B18C-8C9CC857D7A6@yahoo.com> <6669.1551473821@critter.freebsd.dk> <210dfd0f50ee6b1149c914ee503502654eb5f328.camel@freebsd.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <210dfd0f50ee6b1149c914ee503502654eb5f328.camel@freebsd.org> User-Agent: Mutt/1.11.3 (2019-02-01) X-Spam-Status: No, score=-1.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FORGED_GMAIL_RCVD,FREEMAIL_FROM, NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on tom.home X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 02 Mar 2019 10:57:02 -0000 On Fri, Mar 01, 2019 at 02:11:33PM -0700, Ian Lepore wrote: > On Fri, 2019-03-01 at 20:57 +0000, Poul-Henning Kamp wrote: > > -------- > > In message <679402FF-907C-43AF-B18C-8C9CC857D7A6@yahoo.com>, Mark > > Millard via freebsd-hackers writes: > > > > > > I must admit that 2 seconds of interval where the timehands where > > > > not updated is too much. > > > > I have no idea how you got in that situation, but it is very far > > from how timecounters were designed to work. > > > > I wonder if it's fallout from reducing the number of timehands to 2, > which always struck me as a really bad idea. I know of at least one arm > configuration which fails because of it (it takes a combo of a single- > core system, and a pps capture driver that uses hardware latching of > the timer and the polling method for reading the latched value; given > all that, at least 4 sets of timehands are needed to avoid losing PPS > events due to generation changes). Using more than two timehands increases a chance of reader to try to use outdated timehands. In theory, on the hardware with very high inter-core propagation (e.g. with sufficiently large store buffers) it is possible for other CPU to use non-current timehands. More timehands you have, larger is the relative error. If you have very specific configuration which contradicts to the typical modern hardware configuration, I do not see a problem restoring some more timehands entries under a config option.