On Fri, Jun 24, 2016 at 03:03:24PM +0200, Peter Zijlstra wrote: > > Task's last_update_time means this task is detached from fair queue. This > > (re)definition is by all means much better than migrating. No? > > I would maybe redefine it as an up-to-date marker for a migration across > a clock discontinuity. Both CPU migration and group movement suffer from > this, albeit for different reasons. > > In the CPU migration case we simply cannot tell time by our refusal to > acquire the old rq lock. So we age to the last time we 'know' and then > mark it up-to-date. > > For the cgroup move the timelines simply _are_ discontinuous. So we have > to mark it up-to-date after we update it to the instant of detach, such > that when we attach it to the new group we don't try to age it across > the time difference.
Got it. I'm glad to see you worked out all these. It's like I am replying to an email in the last century, sorry, but I was distracted for many other things.
