On Fri, Jun 07, 2019 at 03:00:32PM -0700, Fenghua Yu wrote: > Today, if an application needs to wait for a very short duration > they have to have spinloops. Spinloops consume more power and continue > to use execution resources that could hurt its thread siblings in a core > with hyperthreads. New instructions umonitor, umwait and tpause allow > a low power alternative waiting at the same time could improve the HT > sibling perform while giving it any power headroom. These instructions > can be used in both user space and kernel space. > > A new MSR IA32_UMWAIT_CONTROL allows kernel to set a time limit in > TSC-quanta that prevents user applications from waiting for a long time. > This allows applications to yield the CPU and the user application > should consider using other alternatives to wait.
I'm confused on the purpose of this control; what do we win by limiting this time? > .../ABI/testing/sysfs-devices-system-cpu | 21 ++ > arch/x86/include/asm/cpufeatures.h | 1 + > arch/x86/include/asm/msr-index.h | 4 + > arch/x86/power/Makefile | 1 + > arch/x86/power/umwait.c | 182 ++++++++++++++++++ You seem to miss the arch/x86/lib/delay.c change to use this fancy new stuff for udelay(). I'm thinking that's exactly what TPAUSE is good for.
