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].
