netdev - Re: [PATCH v3 5/6] can: c_can: prepare to up the message objects number

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Date:   Wed, 3 Mar 2021 11:31:10 +0100 (CET)
From:   Dario Binacchi <dariobin@...ero.it>
To:     Marc Kleine-Budde <mkl@...gutronix.de>
Cc:     Kurt Van Dijck <dev.kurt@...dijck-laurijssen.be>,
        linux-kernel@...r.kernel.org,
        Federico Vaga <federico.vaga@...il.com>,
        Alexander Stein <alexander.stein@...tec-electronic.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Oliver Hartkopp <socketcan@...tkopp.net>,
        Vincent Mailhol <mailhol.vincent@...adoo.fr>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        YueHaibing <yuehaibing@...wei.com>,
        Zhang Qilong <zhangqilong3@...wei.com>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v3 5/6] can: c_can: prepare to up the message objects
 number

Hi Marc,

> Il 03/03/2021 10:00 Marc Kleine-Budde <mkl@...gutronix.de> ha scritto:
> 
>  
> On 03.03.2021 09:23:13, Dario Binacchi wrote:
> [...]
> > > > @@ -1205,17 +1203,31 @@ static int c_can_close(struct net_device *dev)
> > > >  	return 0;
> > > >  }
> > > >  
> > > > -struct net_device *alloc_c_can_dev(void)
> > > > +struct net_device *alloc_c_can_dev(int msg_obj_num)
> > > >  {
> > > >  	struct net_device *dev;
> > > >  	struct c_can_priv *priv;
> > > > +	int msg_obj_tx_num = msg_obj_num / 2;
> > > 
> > > IMO, a bigger tx queue is not usefull.
> > > A bigger rx queue however is.
> > 
> > This would not be good for my application. I think it really depends
> > on the type of application. We can probably say that being able to
> > size rx/tx queue would be a useful feature.
> 
> Ok. There is an ethtool interface to configure the size of the RX and TX
> queues. In ethtool it's called the RX/TX "ring" size and you can get it
> via the -g parameter, e.g. here for by Ethernet interface:
> 
> | $ ethtool -g enp0s25
> | Ring parameters for enp0s25:
> | Pre-set maximums:
> | RX:		4096
> | RX Mini:	n/a
> | RX Jumbo:	n/a
> | TX:		4096
> | Current hardware settings:
> | RX:		256
> | RX Mini:	n/a
> | RX Jumbo:	n/a
> | TX:		256
> 
> If I understand correctly patch 6 has some assumptions that RX and TX
> are max 32. To support up to 64 RX objects, you have to convert:
> - u32 -> u64
> - BIT() -> BIT_ULL()
> - GENMASK() -> GENMASK_ULL()
> 
> The register access has to be converted, too. For performance reasons
> you want to do as least as possible. Which is probably the most
> complicated.
> 
> In the flexcan driver I have a similar problem. The driver keeps masks,
> which mailboxes are RX and which TX and I added wrapper functions to
> minimize IO access:
> 
> https://elixir.bootlin.com/linux/v5.11/source/drivers/net/can/flexcan.c#L904
> 
> This should to IMHO into patch 6.
> 
> Adding the ethtool support and making the rings configurable would be a
> separate patch.
> 

I think these features need to be developed in a later series. 
I would stay with the extension to 64 messages equally divided 
between reception and transmission.

Thanks and regards,
Dario

> regards,
> Marc
> 
> -- 
> Pengutronix e.K.                 | Marc Kleine-Budde           |
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