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.