From owner-freebsd-hackers@freebsd.org Tue Oct 27 14:04:12 2015 Return-Path: Delivered-To: freebsd-hackers@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 68665A1EC4D for ; Tue, 27 Oct 2015 14:04:12 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id D4B50107B; Tue, 27 Oct 2015 14:04:11 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kostik@localhost [127.0.0.1]) by kib.kiev.ua (8.15.2/8.15.2) with ESMTPS id t9RE43Pi069729 (version=TLSv1 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO); Tue, 27 Oct 2015 16:04:03 +0200 (EET) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua t9RE43Pi069729 Received: (from kostik@localhost) by tom.home (8.15.2/8.15.2/Submit) id t9RE434G069728; Tue, 27 Oct 2015 16:04:03 +0200 (EET) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Tue, 27 Oct 2015 16:04:03 +0200 From: Konstantin Belousov To: Andriy Gapon Cc: freebsd-hackers , Poul-Henning Kamp , Jung-uk Kim Subject: Re: instability of timekeeping Message-ID: <20151027140403.GB2257@kib.kiev.ua> References: <56261398.60102@FreeBSD.org> <56261FE6.90302@FreeBSD.org> <56274FFC.2000608@FreeBSD.org> <20151021184850.GX2257@kib.kiev.ua> <562F3E2F.2010100@FreeBSD.org> <20151027115810.GU2257@kib.kiev.ua> <562F8109.4050203@FreeBSD.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <562F8109.4050203@FreeBSD.org> User-Agent: Mutt/1.5.24 (2015-08-30) 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=3.4.1 X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on tom.home X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 27 Oct 2015 14:04:12 -0000 On Tue, Oct 27, 2015 at 03:50:01PM +0200, Andriy Gapon wrote: > On 27/10/2015 13:58, Konstantin Belousov wrote: > > On Tue, Oct 27, 2015 at 11:04:47AM +0200, Andriy Gapon wrote: > >> And now another observation. I have C1E option enabled in BIOS. It > >> means that if all cores enter C1 state, then the whole processor > >> is magically placed into a deep C-state (C3, I think). LAPIC timer > >> on this CPU model does not run in the deep C-state. So, I had to > >> disable C1E option to test the LAPIC timer in a useful way. But > >> before actually testing it I first tried to reproduce the problem. As > >> you might have already guessed the problem is gone with that option > >> disabled. Scratching my head to understand the implications of this > >> observation. > > > > Most obvious explanation would be that the latency of wakeup is very large. > > What is the HPET frequency when the jitter occur ? > > > > kern.timecounter.tc.TSC-low.frequency: 1607351869 > kern.eventtimer.et.HPET.frequency: 14318180 > > Or did you mean the actual rate of timer interrupts? Actual rate, and I used the wrong word. Since most likely your eventtimer is not periodic, I mean the next timer interrupt deadline.