On Fri, May 24, 2019 at 5:05 PM Fenghua Yu <fenghua...@intel.com> wrote: > > umonitor, umwait, and tpause are a set of user wait instructions. > > umonitor arms address monitoring hardware using an address. The > address range is determined by using CPUID.0x5. 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. > > The three instructions may be executed at any privilege level. > > The instructions provide power saving method while waiting in > user space. Additionally, they can allow a sibling hyperthread to > make faster progress while this thread is waiting. One example of an > application usage of umwait is when waiting for input data from another > application, such as a user level multi-threaded packet processing > engine. > > Availability of the user wait instructions is indicated by the presence > of the CPUID feature flag WAITPKG CPUID.0x07.0x0:ECX[5]. > > Detailed information on the instructions and CPUID feature WAITPKG flag > can be found in the latest Intel Architecture Instruction Set Extensions > and Future Features Programming Reference and Intel 64 and IA-32 > Architectures Software Developer's Manual. >
Reviewed-by: Andy Lutomirski <l...@kernel.org> > Signed-off-by: Fenghua Yu <fenghua...@intel.com> > Reviewed-by: Ashok Raj <ashok....@intel.com> > --- > arch/x86/include/asm/cpufeatures.h | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/x86/include/asm/cpufeatures.h > b/arch/x86/include/asm/cpufeatures.h > index 75f27ee2c263..b8bd428ae5bc 100644 > --- a/arch/x86/include/asm/cpufeatures.h > +++ b/arch/x86/include/asm/cpufeatures.h > @@ -322,6 +322,7 @@ > #define X86_FEATURE_UMIP (16*32+ 2) /* User Mode Instruction > Protection */ > #define X86_FEATURE_PKU (16*32+ 3) /* Protection Keys > for Userspace */ > #define X86_FEATURE_OSPKE (16*32+ 4) /* OS Protection Keys > Enable */ > +#define X86_FEATURE_WAITPKG (16*32+ 5) /* UMONITOR/UMWAIT/TPAUSE > Instructions */ > #define X86_FEATURE_AVX512_VBMI2 (16*32+ 6) /* Additional AVX512 > Vector Bit Manipulation Instructions */ > #define X86_FEATURE_GFNI (16*32+ 8) /* Galois Field New > Instructions */ > #define X86_FEATURE_VAES (16*32+ 9) /* Vector AES */ > -- > 2.19.1 > -- Andy Lutomirski AMA Capital Management, LLC
