netdev - RE: [PATCH net-next] r8152: divide the tx and rx bottom functions

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Date:   Fri, 16 Aug 2019 10:04:58 +0000
From:   Hayes Wang <hayeswang@...ltek.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     nic_swsd <nic_swsd@...ltek.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH net-next] r8152: divide the tx and rx bottom functions

Eric Dumazet [mailto:eric.dumazet@...il.com]
> Sent: Friday, August 16, 2019 5:27 PM
[...]
> Maybe you would avoid messing with a tasklet (we really try to get rid
> of tasklets in general) using two NAPI, one for TX, one for RX.
> 
> Some drivers already use two NAPI, it is fine.
> 
> This might avoid the ugly dance in r8152_poll(),
> calling napi_schedule(napi) after napi_complete_done() !

The reason is that the USB device couldn't control
the interrupt of USB controller. That is, I couldn't
disable the interrupt before napi_schedule and
enable it after napi_complete_done. If the callback
function occurs during the following timing, it is
possible no one would schedule the napi again.

static int r8152_poll(struct napi_struct *napi, int budget)
{
	struct r8152 *tp = container_of(napi, struct r8152, napi);
	int work_done;

	work_done = rx_bottom(tp, budget);
	bottom_half(tp);

	--> callback occurs here and try to call napi_schedule

	napi_complete_done(napi, work_done)

That is, no tx or rx could be handled unless
something trigger napi_schedule.


Best Regards,
Hayes