Re: [PATCH RESEND v4] sched/fair: Add advisory flag for borrowing a timeslice
- From
- Peter Zijlstra <peterz@infradead.org>
- Date
- 2015-01-13 11:25:34
- Also in
- lkml
- Reply to
- Rik van Riel, 2014-12-23
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.