Re: [PATCH] timers/nohz: Update nohz load even if tick already stopped

[Scott Wood]

On Tue, 2019-11-05 at 13:43 +0100, Peter Zijlstra wrote:
> On Tue, Nov 05, 2019 at 01:30:58AM -0600, Scott Wood wrote:
> > As for the warning in sched_tick_remote(), it seems like a test for time
> > since the last tick on this cpu (remote or otherwise) would be better
> > than
> > relying on curr->se.exec_start, in order to detect things like this.
> 
> I don't think we have a timestamp that is shared between the remote and
> local tick. 

Why wouldn't rq_clock_task() work on the local tick?  It's what
->task_tick() itself uses.

> Also, there is a reason this warning uses the task time
> accounting, there used to be (as in, I can't find it in a hurry) code
> that could not deal with >u32 (~4s) clock updates.

Detecting a 3 second interval between ticks for a given cpu should assert in
a superset of the situations the current check asserts in -- it just avoids
the false negative of exec_runtime getting updated by something other than
the tick.

-Scott