Ping for comments :)
On 9/29/2019 9:57 AM, Xu, Tao3 wrote:
> UMONITOR, UMWAIT and TPAUSE are a set of user wait instructions.
>
> UMONITOR arms address monitoring hardware using an address. A store
> to an address within the specified address range triggers the
> monitoring hardware to wake up the processor waiting in umwait.
>
> UMWAIT instructs the processor to enter an implementation-dependent
> optimized state while monitoring a range of addresses. The optimized
> state may be either a light-weight power/performance optimized state
> (c0.1 state) or an improved power/performance optimized state
> (c0.2 state).
>
> TPAUSE instructs the processor to enter an implementation-dependent
> optimized state c0.1 or c0.2 state and wake up when time-stamp counter
> reaches specified timeout.
>
> Availability of the user wait instructions is indicated by the presence
> of the CPUID feature flag WAITPKG CPUID.0x07.0x0:ECX[5].
>
> The patches enable the umonitor, umwait and tpause features in KVM.
> Because umwait and tpause can put a (psysical) CPU into a power saving
> state, by default we dont't expose it in kvm and provide a capability to
> enable it. Use kvm capability to enable UMONITOR, UMWAIT and TPAUSE when
> QEMU use "-overcommit cpu-pm=on, a VM can use UMONITOR, UMWAIT and TPAUSE
> instructions. If the instruction causes a delay, the amount of time
> delayed is called here the physical delay. The physical delay is first
> computed by determining the virtual delay (the time to delay relative to
> the VM’s timestamp counter). Otherwise, UMONITOR, UMWAIT and TPAUSE cause
> an invalid-opcode exception(#UD).
>
> The release document ref below link:
> https://software.intel.com/sites/default/files/\
> managed/39/c5/325462-sdm-vol-1-2abcd-3abcd.pdf
>
> Changelog:
> v5:
> Remove CPUID_7_0_ECX_WAITPKG if enable_cpu_pm is not set. (Paolo)
> v4:
> Set IA32_UMWAIT_CONTROL 32bits
> v3:
> Simplify the patches, expose user wait instructions when the guest
> has CPUID (Paolo)
> v2:
> Separated from the series
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg549526.html
> Use kvm capability to enable UMONITOR, UMWAIT and TPAUSE when
> QEMU use "-overcommit cpu-pm=on"
> v1:
> Sent out with MOVDIRI/MOVDIR64B instructions patches
>
> Tao Xu (2):
> x86/cpu: Add support for UMONITOR/UMWAIT/TPAUSE
> target/i386: Add support for save/load IA32_UMWAIT_CONTROL MSR
>
> target/i386/cpu.c | 3 ++-
> target/i386/cpu.h | 3 +++
> target/i386/kvm.c | 19 +++++++++++++++++++
> target/i386/machine.c | 20 ++++++++++++++++++++
> 4 files changed, 44 insertions(+), 1 deletion(-)
>