On Thu, Jul 02, 2015 at 07:25:11AM +0800, Yuyang Du wrote:
> And obviously, the idle balancing livelock SHOULD happen: one CPU pulls
> tasks from the other, makes the other idle, and this iterates...
>
> That being said, it is also obvious to prevent the livelock from happening:
> idle pulling until the source rq's nr_running is 1, becuase otherwise we
> just avoid idleness by making another idleness.
Well, ideally the imbalance calculation would be so that it would avoid
this from happening in the first place. Its a 'balance' operation, not a
'steal everything'.
We want to take work -- as we have none -- but we want to ensure that
afterwards we have equal work, ie we're balanced.
So clearly that all is hosed. Now Morten was looking into simplifying
calculate_imbalance() recently.
> On Wed, Jul 01, 2015 at 10:44:04PM +0200, Peter Zijlstra wrote:
> > On Wed, Jul 01, 2015 at 04:55:51PM +0200, Rabin Vincent wrote:
> > > PID: 413 TASK: 8edda408 CPU: 1 COMMAND: "rngd"
> > > task_h_load(): 0 [ = (load_avg_contrib { 0} * cfs_rq->h_load {
> > > 0}) / (cfs_rq->runnable_load_avg { 0} + 1) ]
> > > SE: 8edda450 load_avg_contrib: 0 load.weight: 1024 PARENT:
> > > 8fffbd00 GROUPNAME: (null)
> > > SE: 8fffbd00 load_avg_contrib: 0 load.weight: 2 PARENT:
> > > 8f531f80 GROUPNAME: rngd@hwrng.service
> > > SE: 8f531f80 load_avg_contrib: 0 load.weight: 1024 PARENT:
> > > 8f456e00 GROUPNAME: system-rngd.slice
> > > SE: 8f456e00 load_avg_contrib: 118 load.weight: 911 PARENT:
> > > 00000000 GROUPNAME: system.slice
> >
> > Firstly, a group (parent) load_avg_contrib should never be less than
> > that of its constituent parts, therefore the top 3 SEs should have at
> > least 118 too.
>
> I think the downward is parent,
Ugh, I cannot read. Let me blame it on the heat.
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