----- On Feb 23, 2016, at 8:36 PM, H. Peter Anvin [email protected] wrote: > On 02/23/2016 03:28 PM, Mathieu Desnoyers wrote: >> Hi, >> >> Here is a patchset implementing a cache for the CPU number of the >> currently running thread in user-space. >> >> Benchmarks comparing this approach to a getcpu based on system call on >> ARM show a 44x speedup. They show a 14x speedup on x86-64 compared to >> executing lsl from a vDSO through glibc. >> >> I'm added a man page in the changelog of patch 1/3, which shows an >> example usage of this new system call. >> >> This series is based on v4.5-rc5, submitted for Linux 4.6. >> >> Feedback is welcome, >> > > What is the resulting context switch overhead?
The getcpu_cache only adds code to the thread migration path, and to the resume notifier. The context switch path per se is untouched. I would therefore expect the overhead on context switch to be within the noise, except if stuff like hackbench would be so sensitive to the size of struct task_struct that a single extra pointer added at the end of struct task_struct would throw off the benchmarks. Is that what you are concerned about ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
