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x64: `WAITPKG`-based spinlocks

Open Wunkolo opened this issue 4 years ago • 2 comments

The waitpkg cpuid flag indicates the availability of some user-space instructions for monitoring an address region and waiting for a specific memory-region to be written to, in particular umonitor and umwait. These instructions are found in tremont, sapphire rapids, and alderlake. https://www.felixcloutier.com/x86/umonitor https://www.felixcloutier.com/x86/umwait

I proposed the additions for xbyak here: https://github.com/herumi/xbyak/issues/143

These instructions can possibly be used to accelerate spinlocks.

Wunkolo avatar Apr 03 '22 14:04 Wunkolo

waitpkg instructions have been added to xbyak as of https://github.com/herumi/xbyak/commit/898c354e67313b194efe3a66e0f502ed4dac35ed

Wunkolo avatar Apr 09 '22 20:04 Wunkolo

I've made a draft of this, but I do not currently have the required hardware available to me at the moment to validate that the implementation works or that it is faster than pause. Based on the descriptions though, it should be faster and more optimal in the case of hyper-threading cores and systems with many cores.

Wunkolo avatar Jun 16 '22 00:06 Wunkolo