On Tue, Jan 09, 2018 at 05:44:48AM -0800, Tejun Heo wrote:
> Hello, Paul.
>
> On Mon, Jan 08, 2018 at 08:20:16PM -0800, Paul E. McKenney wrote:
> > OK, so I can put WQ_MEM_RECLAIM on the early boot creation of RCU's
> > workqueue_struct as shown below, right?
>
> Yes, this looks good to me. Just one question.
>
> > +struct workqueue_struct *rcu_gp_workqueue;
> > +
> > void __init rcu_init(void)
> > {
> > int cpu;
> > @@ -4298,6 +4300,10 @@ void __init rcu_init(void)
> > rcu_cpu_starting(cpu);
> > rcutree_online_cpu(cpu);
> > }
> > +
> > + /* Create workqueue for expedited GPs and for Tree SRCU. */
> > + rcu_gp_workqueue = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
> > + WARN_ON(!rcu_gp_workqueue);
>
> The code was previously using both system_power_efficient_wq and
> system_workqueue (for the expedited path). I guess the options were
> either using two workqueues or dropping POWER_EFFICIENT. I have no
> idea how big an impact this will make or whether it'd even be
> noticeable but maybe it'd be worthwhile to mention that in the
> description?
Good point! How about if I change the last paragraph of the commit
log to read as follows?
Thanx, Paul
------------------------------------------------------------------------
This commit also causes SRCU to use this new RCU-specific
workqueue_struct. Note that SRCU's use of workqueues never blocks them
waiting for readers, so this should be safe from a forward-progress
viewpoint. Note that this moves SRCU from system_power_efficient_wq
to a normal workqueue. In the unlikely event that this results in
measurable degradation, a separate power-efficient workqueue will be
creates for SRCU.
