> On Jul 22, 2019, at 2:07 PM, Peter Zijlstra <pet...@infradead.org> wrote: > > On Thu, Jul 18, 2019 at 10:41:10AM -0700, Nadav Amit wrote: >> The current_task is supposed to be constant in each thread and therefore >> does not need to be reread. There is already an attempt to cache it >> using inline assembly, using this_cpu_read_stable(), which hides the >> dependency on the read memory address. > > Is that what it does?!, I never quite could understand > percpu_stable_op().
That’s my understanding. I am not too pleased that I could not come up with a general alternative to this_cpu_read_stable(), mainly because gcc does not provide a way to get the type without the segment qualifier. Anyhow, “current” seems to be the main pain-point. I think a similar const-alias approach can also be used for stuff like boot_cpu_has(). I have some patches for that somewhere, but the impact is smaller. I do see some small, but measurable performance improvements with this series. I’ll try to incorporate them in v1 once I have time.
