From owner-freebsd-hackers@freebsd.org  Tue Oct 27 13:51:08 2015
Return-Path: <owner-freebsd-hackers@freebsd.org>
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 C2DA2A1E7A2
 for <freebsd-hackers@mailman.ysv.freebsd.org>;
 Tue, 27 Oct 2015 13:51:08 +0000 (UTC) (envelope-from avg@FreeBSD.org)
Received: from citadel.icyb.net.ua (citadel.icyb.net.ua [212.40.38.140])
 by mx1.freebsd.org (Postfix) with ESMTP id D0AF01369;
 Tue, 27 Oct 2015 13:51:07 +0000 (UTC) (envelope-from avg@FreeBSD.org)
Received: from porto.starpoint.kiev.ua (porto-e.starpoint.kiev.ua
 [212.40.38.100])
 by citadel.icyb.net.ua (8.8.8p3/ICyb-2.3exp) with ESMTP id PAA20802;
 Tue, 27 Oct 2015 15:50:59 +0200 (EET) (envelope-from avg@FreeBSD.org)
Received: from localhost ([127.0.0.1])
 by porto.starpoint.kiev.ua with esmtp (Exim 4.34 (FreeBSD))
 id 1Zr4eQ-000HBQ-Qd; Tue, 27 Oct 2015 15:50:58 +0200
Subject: Re: instability of timekeeping
To: Konstantin Belousov <kostikbel@gmail.com>
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>
Cc: freebsd-hackers <freebsd-hackers@FreeBSD.org>,
 Poul-Henning Kamp <phk@phk.freebsd.dk>, Jung-uk Kim <jkim@FreeBSD.org>
From: Andriy Gapon <avg@FreeBSD.org>
Message-ID: <562F8109.4050203@FreeBSD.org>
Date: Tue, 27 Oct 2015 15:50:01 +0200
User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:38.0) Gecko/20100101
 Thunderbird/38.3.0
MIME-Version: 1.0
In-Reply-To: <20151027115810.GU2257@kib.kiev.ua>
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: 7bit
X-BeenThere: freebsd-hackers@freebsd.org
X-Mailman-Version: 2.1.20
Precedence: list
List-Id: Technical Discussions relating to FreeBSD
 <freebsd-hackers.freebsd.org>
List-Unsubscribe: <https://lists.freebsd.org/mailman/options/freebsd-hackers>, 
 <mailto:freebsd-hackers-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-hackers/>
List-Post: <mailto:freebsd-hackers@freebsd.org>
List-Help: <mailto:freebsd-hackers-request@freebsd.org?subject=help>
List-Subscribe: <https://lists.freebsd.org/mailman/listinfo/freebsd-hackers>, 
 <mailto:freebsd-hackers-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Tue, 27 Oct 2015 13:51:08 -0000

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?

-- 
Andriy Gapon