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Date: Tue, 27 Oct 2015 13:58:10 +0200
From: Konstantin Belousov <kostikbel@gmail.com>
To: Andriy Gapon <avg@FreeBSD.org>
Cc: freebsd-hackers <freebsd-hackers@FreeBSD.org>,
 Poul-Henning Kamp <phk@phk.freebsd.dk>, Jung-uk Kim <jkim@FreeBSD.org>
Subject: Re: instability of timekeeping
Message-ID: <20151027115810.GU2257@kib.kiev.ua>
References: <56261398.60102@FreeBSD.org> <56261FE6.90302@FreeBSD.org>
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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 ?