From owner-freebsd-hackers@freebsd.org Sat Mar 2 14:17:18 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 A5A96152522E; Sat, 2 Mar 2019 14:17:18 +0000 (UTC) (envelope-from phk@critter.freebsd.dk) Received: from phk.freebsd.dk (phk.freebsd.dk [130.225.244.222]) by mx1.freebsd.org (Postfix) with ESMTP id 3B905685BF; Sat, 2 Mar 2019 14:17:17 +0000 (UTC) (envelope-from phk@critter.freebsd.dk) Received: from critter.freebsd.dk (v-critter.freebsd.dk [192.168.55.3]) by phk.freebsd.dk (Postfix) with ESMTP id A76AB202563B; Sat, 2 Mar 2019 14:17:11 +0000 (UTC) Received: from critter.freebsd.dk (localhost [127.0.0.1]) by critter.freebsd.dk (8.15.2/8.15.2) with ESMTPS id x22EHBQ4009995 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Sat, 2 Mar 2019 14:17:11 GMT (envelope-from phk@critter.freebsd.dk) Received: (from phk@localhost) by critter.freebsd.dk (8.15.2/8.15.2/Submit) id x22EHAxh009994; Sat, 2 Mar 2019 14:17:10 GMT (envelope-from phk) To: Konstantin Belousov cc: Ian Lepore , 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] In-reply-to: <20190302105652.GD68879@kib.kiev.ua> From: "Poul-Henning Kamp" 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> <20190302105652.GD68879@kib.kiev.ua> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <9992.1551536230.1@critter.freebsd.dk> Date: Sat, 02 Mar 2019 14:17:10 +0000 Message-ID: <9993.1551536230@critter.freebsd.dk> X-Rspamd-Queue-Id: 3B905685BF X-Spamd-Bar: ------ Authentication-Results: mx1.freebsd.org X-Spamd-Result: default: False [-6.93 / 15.00]; NEURAL_HAM_MEDIUM(-1.00)[-1.000,0]; NEURAL_HAM_SHORT(-0.93)[-0.930,0]; REPLY(-4.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000,0] 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 14:17:18 -0000 -------- In message <20190302105652.GD68879@kib.kiev.ua>, Konstantin Belousov writes: >Using more than two timehands increases a chance of reader to try to >use outdated timehands. No, using only two timehands increase the chance that the reader tries to use the timehand which is being updated. As long as the reader does not use the timehand being updated, using a one or two generations old timehand is OK. At worst a frequency change happened since then, in which case the timestamp will be "delta-f * delta-t" wrong. Delta-f is in 1e-7 territory on a system running ntpd(8), so this is below noise level for anything but high-precision timekeeping. The target-value for delta-t was "a few milliseconds" when I wrote timecounters, if somebody has changed that since, I hope they did their math first. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.