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Re: [Qemu-devel] [PATCH] hw/arm/virt: Add always-on property to the virt
From: |
Andrew Jones |
Subject: |
Re: [Qemu-devel] [PATCH] hw/arm/virt: Add always-on property to the virt board timer |
Date: |
Wed, 20 Jan 2016 15:01:21 +0100 |
User-agent: |
Mutt/1.5.23.1 (2014-03-12) |
On Tue, Jan 19, 2016 at 07:48:14PM +0100, Andrew Jones wrote:
> On Tue, Jan 19, 2016 at 01:43:07PM +0000, Marc Zyngier wrote:
> > >> On Tue, Jan 19, 2016 at 01:37:16PM +0100, Andrew Jones wrote:
> > > OK, CCing him. One thing I see is that without this change we're
> > > currently setting the clock feature CLOCK_EVT_FEAT_C3STOP, even though
> > > it's not true. Having that set may disable the oneshot capabilityj
> > > necessary to switch to nohz mode? I'll just stop there with my
> > > speculation though, so Marc won't have to correct too much...
> >
> > You're spot on. See 82a5619 in the kernel tree. When I did a similar
> > change in kvmtool, I saw a massive reduction in the number of timer
> > interrupts injected (specially when the number of vcpu is relatively high).
> >
> > This also have interesting benefits when running on a model, where
> > you're trying to squeeze the last bits of "performance" from the monster...
> >
>
> Hmm, I'm probably testing this wrong, but I don't see any difference in
> the number of injected timer interrupts. My guest, which I boot with
> UEFI, has
>
> CONFIG_ARM_ARCH_TIMER=y
> CONFIG_ARM_ARCH_TIMER_EVTSTREAM=y
> CONFIG_ARM_TIMER_SP804=y
> CONFIG_HIGH_RES_TIMERS=y
> CONFIG_TICK_ONESHOT=y
> CONFIG_NO_HZ_COMMON=y
> # CONFIG_HZ_PERIODIC is not set
> CONFIG_NO_HZ_IDLE=y
> # CONFIG_NO_HZ_FULL is not set
> CONFIG_NO_HZ=y
> CONFIG_HZ_1000=y
> CONFIG_HZ=1000
>
> I've boot a guest using DT with and without this patch
>
> ---WITHOUT---
>
> # ls /proc/device-tree/timer
> compatible interrupts name
> # cat /proc/interrupts
> CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6
> CPU7
> 3: 6958 5766 5166 5187 5576 5129 4695
> 4398 GIC 27 Edge arch_timer
> # sleep 120 && cat /proc/interrupts
> CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6
> CPU7
> 3: 7557 5986 5487 5265 6232 5868 5464
> 4438 GIC 27 Edge arch_timer
>
> ---WITH---
>
> # ls /proc/device-tree/timer
> always-on compatible interrupts name
> # cat /proc/interrupts
> CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6
> CPU7
> 3: 7005 6080 4996 5391 5165 5257 4930
> 4844 GIC 27 Edge arch_timer
> # sleep 120 && cat /proc/interrupts
> CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6
> CPU7
> 3: 7523 6505 5264 6717 5273 5391 5526
> 4901 GIC 27 Edge arch_timer
>
>
>
> And kvm trace data has
>
> ---WITHOUT---
> $ grep kvm_timer_update_irq trace.out | wc -l
> 94336
> ---WITH---
> $ grep kvm_timer_update_irq trace.out | wc -l
> 95838
>
>
Must be how I'm looking, because I just tried kvmtool with/without
Marc's patch that adds always-on, but don't see any reduction of
interrupts there either. I used a defconfig guest kernel. Also,
not that I think it should matter, but my host kernel is 4.4-rc4
based.
I'd like to be able to see a difference with/without this always-on
patch, not because I don't think we should take it anyway, but because
I need a test case for the ACPI counterpart.
Thanks,
drew
- [Qemu-devel] [PATCH] hw/arm/virt: Add always-on property to the virt board timer, Christoffer Dall, 2016/01/19
- Re: [Qemu-devel] [PATCH] hw/arm/virt: Add always-on property to the virt board timer, Andrew Jones, 2016/01/19
- Re: [Qemu-devel] [PATCH] hw/arm/virt: Add always-on property to the virt board timer, Christoffer Dall, 2016/01/19
- Re: [Qemu-devel] [PATCH] hw/arm/virt: Add always-on property to the virt board timer, Andrew Jones, 2016/01/19
- Re: [Qemu-devel] [PATCH] hw/arm/virt: Add always-on property to the virt board timer, Marc Zyngier, 2016/01/19
- Re: [Qemu-devel] [PATCH] hw/arm/virt: Add always-on property to the virt board timer, Andrew Jones, 2016/01/19
- Re: [Qemu-devel] [PATCH] hw/arm/virt: Add always-on property to the virt board timer, Andrew Jones, 2016/01/19
- Re: [Qemu-devel] [PATCH] hw/arm/virt: Add always-on property to the virt board timer,
Andrew Jones <=
- Re: [Qemu-devel] [PATCH] hw/arm/virt: Add always-on property to the virt board timer, Marc Zyngier, 2016/01/20
- Re: [Qemu-devel] [PATCH] hw/arm/virt: Add always-on property to the virt board timer, Andrew Jones, 2016/01/20
- Re: [Qemu-devel] [PATCH] hw/arm/virt: Add always-on property to the virt board timer, Marc Zyngier, 2016/01/20
- Re: [Qemu-devel] [PATCH] hw/arm/virt: Add always-on property to the virt board timer, Andrew Jones, 2016/01/20
- Re: [Qemu-devel] [PATCH] hw/arm/virt: Add always-on property to the virt board timer, Marc Zyngier, 2016/01/20
Re: [Qemu-devel] [PATCH] hw/arm/virt: Add always-on property to the virt board timer, Peter Maydell, 2016/01/19