Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for readers and writers of load_avg

[Waiman Long]

On 12/01/2015 03:49 AM, Peter Zijlstra wrote:
> On Mon, Nov 30, 2015 at 10:55:02PM -0500, Waiman Long wrote:
> > On 11/30/2015 05:09 PM, Peter Zijlstra wrote:
> > > On Mon, Nov 30, 2015 at 02:13:32PM -0500, Waiman Long wrote:
> > > > > This begs the question tough; why are you running a global load in a
> > > > > cgroup; and do we really need to update this for the root cgroup? It
> > > > > seems to me we don't need calc_tg_weight() for the root cgroup, it
> > > > > doesn't need to normalize its weight numbers.
> > > > >
> > > > > That is; isn't this simply a problem we should avoid?
> > > > I didn't use any cgroup in my test setup. Autogroup was enabled, though.
> > > > Booting up a 4.4-rc2 kernel caused sched_create_group() to be called 56
> > > > times.
> > > Yeah, can you kill autogroup and see if that helps? If not, we probably
> > > should add some code to avoid calculating things for the root group.
> > I will try that out tomorrow. However, SCHED_AUTOGROUP was enabled in the
> > distribution kernels. So we still need to look at that with autogroup
> > enabled.
> Meh, or just tell the people that have stupid large machines to use
> noautogroup on boot (its of questionable benefit in the first place imo,
> esp. on servers).

Yes, I was able to recover most of the lost performance by disabling 
autogroup. I did send out a new patch to disable load_avg update for 
root_task_group. I need that for backporting to earlier kernels which 
was forced to update load_avg for every clock tick even for root_task_group.

Cheers,
Longman
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