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Re: [Qemu-devel] [PATCH v2 0/2] kvm: x86 CPU power management
From: |
Marcelo Tosatti |
Subject: |
Re: [Qemu-devel] [PATCH v2 0/2] kvm: x86 CPU power management |
Date: |
Wed, 13 Jun 2018 19:34:53 -0300 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Tue, Jun 12, 2018 at 09:47:11PM +0300, Michael S. Tsirkin wrote:
> This adds ability to expose host CPU power management capabilities to
> guests. For intel guests, this is sufficient for guest to enable
> low power CPU power management. For AMD guests it isn't sufficient,
> deeper C-states are entered using System-IO.
>
> mwait based power management is tied closely to specifics of CPUID,
> making migration challenging. At this point only the non-migrateable
> -cpu host is supported.
>
> With this patch applied, VM latency is within the noise of
> baremetal for some benchmarks.
>
> perf bench sched pipe results:
> Before:
> 6.452 sec
> After:
> 4.382 sec
> Baremetal:
> 4.136 sec
>
> Michael S. Tsirkin (2):
> kvm: support -realtime cpu-pm=on|off
> i386/cpu: make -cpu host support monitor/mwait
>
> include/sysemu/sysemu.h | 1 +
> target/i386/cpu.h | 9 +++++++++
> target/i386/cpu.c | 19 ++++++++++++++-----
> target/i386/kvm.c | 30 ++++++++++++++++++++++++++++++
> vl.c | 6 ++++++
> qemu-options.hx | 9 +++++++--
> 6 files changed, 67 insertions(+), 7 deletions(-)
>
> --
> MST
Hi Michael,
1) Command line option interface
Why is this not an optional cpu feature such as the other features?
-cpu CPU,+mwait
rather than a separate, architecture independent "-realtime cpu-pm=on|off"
command line option?
2) Migration
Isnt it sufficient to check that both CPUID leafs are the same,
to allow migration ?
1. Check that the processor supports MONITOR and MWAIT. If
CPUID.01H:ECX.MONITOR[bit 3] = 1, MONITOR and MWAIT are available at
ring 0.
2. Query the smallest and largest line size that MONITOR uses.
Use CPUID.05H:EAX.smallest[bits 15:0];EBX.largest[bits15:0].