Re: [Qemu-devel] [PATCH v2 0/4] RTC: New logic to emulate RTC

[Paolo Bonzini]

On 02/20/2012 01:24 AM, Zhang, Yang Z wrote:
> Changes in v2:
> Add UIP check logic.
> Add logic that next second tick will occur in exactly 500ms later after 
> setting the clock
> 
> Current RTC emulation uses periodic timer(2 timers per second) to update RTC 
> clock. And it will stop CPU staying at deep C-state for long period. Our 
> experience shows the Pkg C6 residency reduced 6% when running 64 idle guest.
> The following patch stop the two periodic timer and only updating RTC clock 
> when guest try to read it.
> 
> --- 
> Yang Zhang (4):
>       RTC: Update the RTC clock only when reading it
>       RTC: Add RTC update-ended interrupt support
>       RTC: Add alarm support
>       RTC: Add UIP(update in progress) check logic
> 
>       hw/mc146818rtc.c |  447 
> +++++++++++++++++++++++++++++++++++++-----------------
>       1 files changed, 308 insertions(+), 139 deletions(-)
> 
> best regards
> yang
> 
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Thanks, this looks much better!  I'll run it through some tests.

We also should try to keep migration working from older versions using
the load_old callback.

Paolo