[RFC 0/7] Add support to process rx packets in thread

[Hillf Danton]

On Sat, 25 Jul 2020 16:08:41 +0200 Sebastian Gottschall wrote:
> Am 25.07.2020 um 14:25 schrieb Hillf Danton:
> > On Sat, 25 Jul 2020 12:38:00 +0200 Sebastian Gottschall wrote:
> >> you may consider this
> >>
> >> https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1142611.html 
> >>
> >> <https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1142611.html> 
> >>
> > Thanks very much for your link.
> >
> >> years ago someone already wanted to bring this feature upstream, but it
> >> was denied. i already tested this patch the last 2 days and it worked so
> >> far (with some little modifications)
> >> so such a solution existed already and may be considered here
> >
> > I don't see outstanding difference in principle from Paolo's work in
> > 2016 except for the use of kthread_create() and friends because kworker
> > made use of them even before 2016. This is a simpler one as shown by
> > the diff stat in his cover letter.
> >
> i agree. i just can say that i tested this patch recently due this 
> discussion here. and it can be changed by sysfs. but it doesnt work for
> wifi drivers which are mainly using dummy netdev devices. for this i 
> made a small patch to get them working using napi_set_threaded manually 
> hardcoded in the drivers. (see patch bellow)

By CONFIG_THREADED_NAPI, there is no need to consider what you did here
in the napi core because device drivers know better and are responsible
for it before calling napi_schedule(n).

> i also tested various networking drivers. one thing i notice doesnt 
> work. some napi code is used for tx polling. so from my experience this 
> concept just works good for rx with the most drivers.

Drivers are also taking care of the napi::poll cb before calling
netif_threaded_napi_add(), while the core offers napi threads. But these
are the trivial differences from the 2016 RFC AFAICS.

> so far i tested mt76, ath10k and some soc ethernet chipsets with good 
> success. on ath10k i had about 10 - 20% performance gain on multicore 
> systems. using standard iperf3 with 4 parallel streams.

Thanks for sharing the tests.

>
> -5439,7 +5441,7 @@ int napi_set_threaded(struct napi_struct *n, bool
>                  clear_bit(NAPI_STATE_THREADED, &n->state);
> 
>          /* if the device is initializing, nothing todo */
> -       if (test_bit(__LINK_STATE_START, &n->dev->state))
> +       if (test_bit(__LINK_STATE_START, &n->dev->state) && 
> n->dev->reg_state != NETREG_DUMMY)
>                  return 0;
> 
>          napi_thread_stop(n);