Re: [PATCH v4 2/2] io_uring: Add support for napi_busy_poll

[Hao Xu]

On 3/2/22 13:12, Olivier Langlois wrote:
> On Wed, 2022-03-02 at 02:31 +0800, Hao Xu wrote:
> > > +static void io_blocking_napi_busy_loop(struct list_head
> > > *napi_list,
> > > +                                      struct io_wait_queue *iowq)
> > > +{
> > > +       unsigned long start_time =
> > > +               list_is_singular(napi_list) ? 0 :
> > > +               busy_loop_current_time();
> > > +
> > > +       do {
> > > +               if (list_is_singular(napi_list)) {
> > > +                       struct napi_entry *ne =
> > > +                               list_first_entry(napi_list,
> > > +                                                struct napi_entry,
> > > list);
> > > +
> > > +                       napi_busy_loop(ne->napi_id,
> > > io_busy_loop_end, iowq,
> > > +                                      true, BUSY_POLL_BUDGET);
> > > +                       io_check_napi_entry_timeout(ne);
> > > +                       break;
> > > +               }
> > > +       } while (io_napi_busy_loop(napi_list) &&
> > > +                !io_busy_loop_end(iowq, start_time));
> > > +}
> > > +
> > How about:
> >
> > if (list is singular) {
> >
> >       do something;
> >
> >       return;
> >
> > }
> >
> > while (!io_busy_loop_end() && io_napi_busy_loop())
> >
> >       ;
> >
> >
> > Btw, start_time seems not used in singular branch.
> Hao,
>
> it takes me few readings before being able to figure out the idea
> behind your suggestions. Sorry about that!
>
> So, if I get it correctly, you are proposing extract out the singular
> block out of the while loop...
>
> IMHO, this is not a good idea because you could start iterating the
> do/while loop with a multiple entries list that ends up becoming a
> singular list after one or few iterations.
My bad, I get your point now.
> Check what io_napi_busy_loop() is doing...
>
> It does not look like that but a lot thoughts have been put into
> writing io_blocking_napi_busy_loop()...
True.