Re: [RFC PATCH v2 3/5] futex: Throughput-optimized (TO) futexes

From: Waiman Long
Date: Thu Sep 22 2016 - 18:00:07 EST

On 09/22/2016 05:41 PM, Thomas Gleixner wrote:
On Thu, 22 Sep 2016, Davidlohr Bueso wrote:
On Thu, 22 Sep 2016, Waiman Long wrote:

BTW, my initial attempt for the new futex was to use the same workflow as
the PI futexes, but use mutex which has optimistic spinning instead of
Btw, Thomas, do you still have any interest pursuing this for rtmutexes from
-rt into mainline? If so I can resend the patches from a while ago.
Certainly yes. My faint memory tells me that there was some potential issue
due to boosting the owner only if it gets scheduled out, but I might be

It is tricky to add optimistic spinning to rtmutexes because of the need to observe process priorities. It is certainly possible to make the top waiter spin, but then I am not sure how much performance gain with just that.