[Xen-devel] [PATCH] Move RTC from Qemu to HV

["Yang, Xiaowei" <xiaowei.yang@xxxxxxxxx>]

As we know some version of Windows (e.g 32bit Vista and 64bit Win2k3)
use RTC as main periodic timer at 64HZ. Currently RTC is in Qemu which
means its irq may be potentially lost due to Qemu not got scheduled on
time. And it's not sync with Guest TSC (adjusted by TSC_OFFSET). This
will cause many problems, like HVM time goes slow; TSC can't be measured
by cross referring to RTC time. 
This patch moves RTC from Qemu to HV, to resolve these problems. Since
we still need Qemu to fill out RTC ram with (local)time, fd/hd
information, HV will copy this ram from Qemu at startup and then
maintains it by itself. 
Another issue resolved by this patch is Windows which use RTC as
periodic timer hangs at login screen because there are no resources to
wait it up after it calls halt. After moving, RTC timer will wake it. 
One extra benefit is that Vista responses faster. It can be explained by
fewer IO port access cost and more accurate RTC time, which Vista may
use to refresh screen.

Thanks, 
Xiaowei

Attachment: rtc4.patch
Description: rtc4.patch

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