Re: [PATCH RESEND v4] sched/fair: Add advisory flag for borrowing a timeslice

On Tue, Dec 23, 2014 at 01:46:58PM -0500, Rik van Riel wrote:

An uncontended futex is taken without ever going into kernel
space. Adaptive spinning allows short duration futexes to be
taken without going into kernel space.

The going into kernel is a red herring afaict, a no-op syscall costs ~180
cycles or something like that. So sure you can do a wee spin (~90 cycles
to try and amortize that), but I really doubt that this is the problem.