On Thu, Aug 13, 2020 at 09:36:52PM +1000, Daniel Axtens wrote:
> Hi,
>
> >> Seem like this could simply use a copy_to_user to further simplify
> >> things?
> >
> > I'll benchmark it and find out.
>
> I tried this:
>
> for (walk = head; walk; walk = walk->next) {
> - struct pollfd *fds = walk->entries;
> - int j;
> -
> - for (j = 0; j < walk->len; j++, ufds++)
> - if (__put_user(fds[j].revents, &ufds->revents))
> - goto out_fds;
> + if (copy_to_user(ufds, walk->entries,
> + sizeof(struct pollfd) * walk->len))
> + goto out_fds;
> + ufds += walk->len;
> }
>
> With that approach, the poll2 microbenchmark (which polls 128 fds) is
> about as fast as v1.
>
> However, the poll1 microbenchmark, which polls just 1 fd, regresses a
> touch (<1% - ~2%) compared to the current code, although it's largely
> within the noise. Thoughts?
I'd go with copy_to_user() here; post such variant and I'll throw it into
-next after -rc1.
