lkml.org 
[lkml]   [2018]   [Apr]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: NO_HZ_FULL and tick running within a reasonable amount of time
On Mon, Apr 02, 2018 at 03:04:38PM -0700, Paul E. McKenney wrote:

> The WARN_ON_ONCE() triggering is this guy:
>
> delta = rq_clock_task(rq) - curr->se.exec_start;
> WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3);
>
> But given that ->se.exec_start is zeroed from time to time, for example,
> in migrate_task_rq_fair(), I am a bit suspicious of this check.
>
> What am I missing here?

We clear it on migration, but set it when we schedule a task back in.
The above checks that the 'current' task of that CPU had a tick at least
3 seconds ago (to ensure tasks don't go too long without ticks).

The 'current' task is obviously scheduled in and thus must have !0
exec_start time.

\
 
 \ /
  Last update: 2018-04-03 11:23    [W:0.065 / U:0.924 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site