linux-kernel - Re: [PATCH 02/15] can: m_can: Wakeup net queue once tx was issued

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Date:   Wed, 14 Dec 2022 10:18:20 +0100
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Markus Schneider-Pargmann <msp@...libre.com>
Cc:     Chandrasekar Ramakrishnan <rcsekar@...sung.com>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Vincent Mailhol <mailhol.vincent@...adoo.fr>
Subject: Re: [PATCH 02/15] can: m_can: Wakeup net queue once tx was issued

On 14.12.2022 10:14:06, Markus Schneider-Pargmann wrote:
> Hi Marc,
> 
> On Wed, Nov 30, 2022 at 06:21:00PM +0100, Marc Kleine-Budde wrote:
> > On 16.11.2022 21:52:55, Markus Schneider-Pargmann wrote:
> > > Currently the driver waits to wakeup the queue until the interrupt for
> > > the transmit event is received and acknowledged. If we want to use the
> > > hardware FIFO, this is too late.
> > > 
> > > Instead release the queue as soon as the transmit was transferred into
> > > the hardware FIFO. We are then ready for the next transmit to be
> > > transferred.
> > 
> > If you want to really speed up the TX path, remove the worker and use
> > the spi_async() API from the xmit callback, see mcp251xfd_start_xmit().
> > 
> > Extra bonus if you implement xmit_more() and transfer more than 1 skb
> > per SPI transfer.
> 
> Just a quick question here, I mplemented a xmit_more() call and I am
> testing it right now, but it always returns false even under high
> pressure. The device has a txqueuelen set to 1000. Do I need to turn
> some other knob for this to work?

AFAIK you need BQL support: see 0084e298acfe ("can: mcp251xfd: add BQL support").

The etas_es58x driver implements xmit_more(), I added the Author Vincent
on Cc.

Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
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