[Qemu-devel] [PATCH v3 0/7] RTC: New logic to emulate RTC

[Qemu-devel] [PATCH v3 0/7] RTC: New logic to emulate RTC

[Zhang, Yang Z]

Changes in v3:
Rebase to latest head.
Remove the logic to update time format when DM bit changed.
Allow to migrate from old version.
Solve the async when reading UF and UIP

Changes in v2:
Add UIP check logic.
Add logic that next second tick will occur in exactly 500ms later after reset divider

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 (7):
	RTC: Remove the logic to update time format when DM bit changed
	RTC: Update the RTC clock only when reading it
	RTC: Add UIP(update in progress) check logic
	RTC: Set internal millisecond register to 500ms when reset divider
	RTC: Add RTC update-ended interrupt support
	RTC: Add alarm support
	RTC: Allow to migrate from old version

	hw/mc146818rtc.c |  427 ++++++++++++++++++++++++++++++++++-------------------
 	1 files changed, 274 insertions(+), 153 deletions(-)

best regards
yang

Re: [Qemu-devel] [PATCH v3 0/7] RTC: New logic to emulate RTC

[Zhang, Yang Z]

Is there any comments with the version 3?

best regards
yang

> -----Original Message-----
> From: Zhang, Yang Z
> Sent: Friday, March 02, 2012 2:59 PM
> To: qemu-devel@nongnu.org
> Cc: Jan Kiszka; kvm@vger.kernel.org; kvm@vger.kernel.org; aliguori@us.ibm.com;
> Paolo Bonzini; Marcelo Tosatti
> Subject: [PATCH v3 0/7] RTC: New logic to emulate RTC
> 
> Changes in v3:
> Rebase to latest head.
> Remove the logic to update time format when DM bit changed.
> Allow to migrate from old version.
> Solve the async when reading UF and UIP
> 
> Changes in v2:
> Add UIP check logic.
> Add logic that next second tick will occur in exactly 500ms later after reset divider
> 
> 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 (7):
> 	RTC: Remove the logic to update time format when DM bit changed
> 	RTC: Update the RTC clock only when reading it
> 	RTC: Add UIP(update in progress) check logic
> 	RTC: Set internal millisecond register to 500ms when reset divider
> 	RTC: Add RTC update-ended interrupt support
> 	RTC: Add alarm support
> 	RTC: Allow to migrate from old version
> 
> 	hw/mc146818rtc.c |  427
> ++++++++++++++++++++++++++++++++++-------------------
>  	1 files changed, 274 insertions(+), 153 deletions(-)
> 
> best regards
> yang

Re: [Qemu-devel] [PATCH v3 0/7] RTC: New logic to emulate RTC

[Paolo Bonzini]

Il 14/03/2012 01:00, Zhang, Yang Z ha scritto:
> Is there any comments with the version 3?

Can you explain why you dropped the logic to set the timer to the next
event?

Paolo

Re: [Qemu-devel] [PATCH v3 0/7] RTC: New logic to emulate RTC

[Zhang, Yang Z]

> -----Original Message-----
> From: Paolo Bonzini [mailto:pbonzini@redhat.com]
> Sent: Wednesday, March 14, 2012 4:35 PM
> To: Zhang, Yang Z
> Cc: qemu-devel@nongnu.org; Jan Kiszka; kvm@vger.kernel.org;
> aliguori@us.ibm.com; Marcelo Tosatti
> Subject: Re: [PATCH v3 0/7] RTC: New logic to emulate RTC
> 
> Il 14/03/2012 01:00, Zhang, Yang Z ha scritto:
> > Is there any comments with the version 3?
> 
> Can you explain why you dropped the logic to set the timer to the next
> event?
Do you mean why I change the rtc logic? The reason is that: When a guest is idle, the main activity inside qemu is the rtc update timer(2 per second). In our experience(running 64 rhel6u1 guests), it will decrease pkg C6 residency about 6%(6% means 2 watts in my box). And normally, the guest will not use the update-end interrupt and alarm. So there has no need to run a periodic timer when guest isn't using it. 

best regards
yang

Re: [Qemu-devel] [PATCH v3 0/7] RTC: New logic to emulate RTC

[Paolo Bonzini]

Il 14/03/2012 09:52, Zhang, Yang Z ha scritto:
>>>>> Is there any comments with the version 3?
>>> 
>>> Can you explain why you dropped the logic to set the timer to the
>>> next event?
> Do you mean why I change the rtc logic? The reason is that: When a
> guest is idle, the main activity inside qemu is the rtc update
> timer(2 per second). In our experience(running 64 rhel6u1 guests), it
> will decrease pkg C6 residency about 6%(6% means 2 watts in my box).
> And normally, the guest will not use the update-end interrupt and
> alarm. So there has no need to run a periodic timer when guest isn't
> using it.

No, why you're keeping roughly the same logic as current QEMU, instead
of the more radical changes that were in v2.

Paolo

Re: [Qemu-devel] [PATCH v3 0/7] RTC: New logic to emulate RTC

[Zhang, Yang Z]

> -----Original Message-----
> From: Paolo Bonzini [mailto:pbonzini@redhat.com]
> Sent: Wednesday, March 14, 2012 4:54 PM
> To: Zhang, Yang Z
> Cc: qemu-devel@nongnu.org; Jan Kiszka; kvm@vger.kernel.org;
> aliguori@us.ibm.com; Marcelo Tosatti
> Subject: Re: [PATCH v3 0/7] RTC: New logic to emulate RTC
> 
> Il 14/03/2012 09:52, Zhang, Yang Z ha scritto:
> >>>>> Is there any comments with the version 3?
> >>>
> >>> Can you explain why you dropped the logic to set the timer to the
> >>> next event?
> > Do you mean why I change the rtc logic? The reason is that: When a
> > guest is idle, the main activity inside qemu is the rtc update
> > timer(2 per second). In our experience(running 64 rhel6u1 guests), it
> > will decrease pkg C6 residency about 6%(6% means 2 watts in my box).
> > And normally, the guest will not use the update-end interrupt and
> > alarm. So there has no need to run a periodic timer when guest isn't
> > using it.
> 
> No, why you're keeping roughly the same logic as current QEMU, instead
> of the more radical changes that were in v2.
You are right. Actually, the v4 is ready and it uses the same logic with v2. Since I have other high priority task in hand, I don't test v4 too much. So i plan to delay it for a while and hope v3 can be accepted before v4 is ready.
If you really doesn't like the v3, I will pay more effort in v4 and will send out it ASAP. :)

best regards
yang

Re: [Qemu-devel] [PATCH v3 0/7] RTC: New logic to emulate RTC

[Paolo Bonzini]

Il 15/03/2012 01:06, Zhang, Yang Z ha scritto:
> You are right. Actually, the v4 is ready and it uses the same logic
> with v2. Since I have other high priority task in hand, I don't test
> v4 too much. So i plan to delay it for a while and hope v3 can be
> accepted before v4 is ready. If you really doesn't like the v3, I
> will pay more effort in v4 and will send out it ASAP. :)

Thanks, that would be great!

Paolo