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

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Message-ID: <20221214101830.vmujo3js66aozik2@blmsp>
Date:   Wed, 14 Dec 2022 11:18:30 +0100
From:   Markus Schneider-Pargmann <msp@...libre.com>
To:     Marc Kleine-Budde <mkl@...gutronix.de>
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 Wed, Dec 14, 2022 at 10:22:01AM +0100, Marc Kleine-Budde wrote:
> On 14.12.2022 10:18:20, Marc Kleine-Budde wrote:
> > 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.
> 
> Have a look at netdev_queue_set_dql_min_limit() in the etas driver.

Thank you, I need to implement BQL, I wasn't aware of that. I may need
to delay this a bit just to get some feedback on the current state of my
patches, so I know what I need to work on first.

But it seems to be just accounting... Anyways, thank you :)

Best,
Markus