Re: RFC on fixing mutex spinning on owner

From: Steven Rostedt
Date: Thu Mar 17 2016 - 08:06:39 EST

On Thu, 17 Mar 2016 12:16:11 +0100 (CET)
Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:

> On Thu, 17 Mar 2016, Peter Zijlstra wrote:
> > Also, maybe the tracer should measure the time from need_resched()
> > getting true until the next preemption point, instead of the entire time
> > preemption was disabled. Which would avoid the entire issue altogether.
> Well, that only gives you the information on a actual preemption, but not
> information about long preempt disabled regions which can cause a problem
> eventually.

Actually, I was thinking the reverse. If need_resched() is called and
is false, then do a reset of the preemption time. But if need_resched()
is true, then do nothing, as that would measure the total time preempt
disable was set and a task could not schedule.

Question is, should this be a hook and each location audited, or add
this to need_resched() itself?

-- Steve