linux-kernel - Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with sched_domain

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Date:	Wed, 11 May 2016 19:04:21 +0100
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org, clm@...com,
	mgalbraith@...e.de, tglx@...utronix.de, fweisbec@...il.com
Subject: Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with
 sched_domain_shared

On Wed, 11 May, at 07:37:52PM, Peter Zijlstra wrote:
> On Wed, May 11, 2016 at 12:55:56PM +0100, Matt Fleming wrote:
> 
> > This breaks my POWER7 box which presumably doesn't have SD_SHARE_PKG_RESOURCES,
> 
> > index 978b3ef2d87e..d27153adee4d 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -7920,7 +7920,8 @@ static inline void set_cpu_sd_state_busy(void)
> >  		goto unlock;
> >  	sd->nohz_idle = 0;
> >  
> > -	atomic_inc(&sd->shared->nr_busy_cpus);
> > +	if (sd->shared)
> > +		atomic_inc(&sd->shared->nr_busy_cpus);
> >  unlock:
> >  	rcu_read_unlock();
> >  }
> 
> 
> Ah, no, the problem is that while it does have SHARE_PKG_RESOURCES (in
> its SMT domain -- SMT threads share all cache after all), I failed to
> connect the sched_domain_shared structure for it.
> 
> Does something like this also work?

Yep, it does.