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From: | Anthony Liguori |
Subject: | Re: [Qemu-devel] [PATCH 1/4] xen: introduce mc146818rtcxen |
Date: | Mon, 21 Nov 2011 14:49:32 -0600 |
User-agent: | Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.21) Gecko/20110831 Lightning/1.0b2 Thunderbird/3.1.13 |
On 11/20/2011 08:53 AM, Avi Kivity wrote:
On 11/18/2011 04:54 PM, Anthony Liguori wrote:Thinking more about it, I think this entire line of thinking is wrong (including mine) :-) The problem you're trying to solve is that the RTC fires two 1 second timers regardless of whether the guest is reading the wall clock time, right? And since wall clock time is never read from the QEMU RTC in Xen, it's a huge waste? The Right Solution would be to modify the RTC emulation such that it did a qemu_get_clock() during read of the CMOS registers in order to ensure the time was up to date (instead of using 1 second timers). Then the timers wouldn't even exist anymore.That would make host time adjustments (suspend/resume) be reflected in the guest.
qemu_get_clock(rtc_clock)It depends on what clock rtc_clock is tied too. If it's tied to vm_clock, it won't be affected.
Not sure if that's good or bad, but it's different.
Doing this wouldn't change the behavior. I presume you were confusing qemu_get_clock() with qemu_get_timedate().
But our current default behavior has the characteristic that you're concerned about. It's was a conscious decision. See:
commit 6875204c782e7c9aa5c28f96b2583fd31c50468f Author: Jan Kiszka <address@hidden> Date: Tue Sep 15 13:36:04 2009 +0200 Enable host-clock-based RTC Regards, Anthony Liguori
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