On Thu, Mar 17, 2016 at 08:06:29AM -0400, Steven Rostedt wrote:

On Thu, 17 Mar 2016 12:16:11 +0100 (CET)
Thomas Gleixner [off-list ref] wrote:

quoted

On Thu, 17 Mar 2016, Peter Zijlstra wrote:

quoted

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?

Is anybody calling need_resched() and then not doing anything with the
value?