Re: [PATCH 8/9] padata: unbind parallel jobs from specific CPUs

[Daniel Jordan]

On 8/22/19 12:13 AM, Herbert Xu wrote:
> On Mon, Aug 12, 2019 at 08:52:23PM -0400, Daniel Jordan wrote:
> > @@ -191,22 +184,25 @@ static struct padata_priv *padata_get_next(struct parallel_data *pd)
> >   		padata = list_entry(reorder->list.next,
> >   				    struct padata_priv, list);
> >   
> > -		list_del_init(&padata->list);
> > -		atomic_dec(&pd->reorder_objects);
> > +		/*
> > +		 * The check fails in the unlikely event that two or more
> > +		 * parallel jobs have hashed to the same CPU and one of the
> > +		 * later ones finishes first.
> > +		 */
> > +		if (padata->seq_nr == pd->processed) {
> > +			list_del_init(&padata->list);
> > +			atomic_dec(&pd->reorder_objects);
>
> Now that you've changed the test for whether there is work to be
> done you also need to update the code at the end of padata_reorder
> that checks whether there is work to do.  Otherwise we can end up
> in a busy loop that just wastes CPU cycles.

So we can, thanks for catching that.