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Date: Tue, 15 Sep 2009 18:50:41 +0100
From: Jamie Lokier <jamie@shareable.org>
Message-ID: <20090915175041.GA2786@shareable.org>
References: <20090915113603.8313.49563.stgit@mchn012c.ww002.siemens.net>
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In-Reply-To: <20090915113603.8313.49563.stgit@mchn012c.ww002.siemens.net>
Subject: [Qemu-devel] Re: [PATCH v3 0/5] Improve PC RTC emulation
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To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Blue Swirl <blauwirbel@gmail.com>, Dor Laor <dlaor@redhat.com>, Anthony Liguori <aliguori@us.ibm.com>, Glauber Costa <glommer@redhat.com>, qemu-devel@nongnu.org

Jan Kiszka wrote:
> The aim of this series is to allow using the emulated PC RTC (MC146818)
> as a reliable time source for guests. This is particularly useful if the
> host runs NTP or has otherwise access to an accurate clock while the
> guest has not (no network, impossible to add an NTP implementation
> etc.).

I approve of these patches.

But still, how exactly is it useful, without NTP?  Afaik, Linux does
not read the RTC except once at boot time, so it probably still needs
NTP or something like it to have reliable time.  However, it does
_write_ the RTC every 11 minutes if running NTP - does that affect the
emulated behaviour?  Or does the emulated RTC ignore writes?

Do any other OSes read the RTC more than once after boot?

-- Jamie