linux-kernel - RE: [EXT] Re: [PATCH net-next v2 3/4] octeon_ep: implement xmit

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Date:   Fri, 27 Oct 2023 11:25:16 +0000
From:   Shinas Rasheed <srasheed@...vell.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Haseeb Gani <hgani@...vell.com>,
        Vimlesh Kumar <vimleshk@...vell.com>,
        "egallen@...hat.com" <egallen@...hat.com>,
        "mschmidt@...hat.com" <mschmidt@...hat.com>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "horms@...nel.org" <horms@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "wizhao@...hat.com" <wizhao@...hat.com>,
        "konguyen@...hat.com" <konguyen@...hat.com>,
        Veerasenareddy Burru <vburru@...vell.com>,
        Sathesh B Edara <sedara@...vell.com>
Subject: RE: [EXT] Re: [PATCH net-next v2 3/4] octeon_ep: implement xmit_more
 in transmit



> -----Original Message-----
> From: Jakub Kicinski <kuba@...nel.org>
> Sent: Thursday, October 26, 2023 8:15 PM
> To: Shinas Rasheed <srasheed@...vell.com>
> Cc: netdev@...r.kernel.org; linux-kernel@...r.kernel.org; Haseeb Gani
> <hgani@...vell.com>; Vimlesh Kumar <vimleshk@...vell.com>;
> egallen@...hat.com; mschmidt@...hat.com; pabeni@...hat.com;
> horms@...nel.org; davem@...emloft.net; wizhao@...hat.com;
> konguyen@...hat.com; Veerasenareddy Burru <vburru@...vell.com>;
> Sathesh B Edara <sedara@...vell.com>; Eric Dumazet
> <edumazet@...gle.com>
> Subject: Re: [EXT] Re: [PATCH net-next v2 3/4] octeon_ep: implement
> xmit_more in transmit
> 
> On Thu, 26 Oct 2023 07:57:54 +0000 Shinas Rasheed wrote:
> > >The recommended way of implementing 'driver flow control'
> > is to stop the queue once next packet may not fit, and then use
> > netif_xmit_stopped() when deciding whether we need to flush or we can
> > trust xmit_more. see
> > https://urldefense.proofpoint.com/v2/url?u=https-
> 3A__www.kernel.org_doc_html_next_networking_driver.html-23transmit-
> 2Dpath-2Dguidelines&d=DwICAg&c=nKjWec2b6R0mOyPaz7xtfQ&r=1OxLD4y-
> oxrlgQ1rjXgWtmLz1pnaDjD96sDq-
> cKUwK4&m=FyJHTb5Z2u9DTFSYPU38S5kPcP5KvwGWzY-
> DPcqOl1gdnm7ToZhTFpyvhLMqh1hd&s=dBMmwfWKAi0UH3nrz7j9kYnAodDj
> uN3LZ5tC2aL_Prs&e=
> >
> > >> In the skeleton code above, as I understand each tx desc holds a skb frag
> and hence there can be possibility of receiving a full-sized skb, stopping the
> queue but on receiving another normal skb we should observe our queue to
> be stopped. This doesn't arise in our case as even if the skb is full-sized, it will
> only use a single tx descriptor so we can be sure if queue has been stopped,
> the write index will only be updated once posted (and read) tx descriptors
> are processed in napi context and queues awoken.
> >
> > Please correct me if I'm wrong anywhere (sorry if so) to further my
> understanding, and again thanks for your time!
> 
> Could you please do some training on how to use normal / mailing list
> style email at Marvell? Multiple people from Marvell can't quote
> replies correctly, it makes it hard to have a conversation and help
> y'all.
Hi Jacub, apologizing for format errors on my part, will try to rectify in coming mails. Sorry again.


> -----Original Message-----
> From: Eric Dumazet <edumazet@...gle.com>
> Sent: Thursday, October 26, 2023 1:59 PM
> To: Shinas Rasheed <srasheed@...vell.com>
> Cc: Jakub Kicinski <kuba@...nel.org>; netdev@...r.kernel.org; linux-
> kernel@...r.kernel.org; Haseeb Gani <hgani@...vell.com>; Vimlesh Kumar
> <vimleshk@...vell.com>; egallen@...hat.com; mschmidt@...hat.com;
> pabeni@...hat.com; horms@...nel.org; davem@...emloft.net;
> wizhao@...hat.com; konguyen@...hat.com; Veerasenareddy Burru
> <vburru@...vell.com>; Sathesh B Edara <sedara@...vell.com>
> Subject: Re: [EXT] Re: [PATCH net-next v2 3/4] octeon_ep: implement
> xmit_more in transmit
> 
> Fact that octep_start_xmit() can return NETDEV_TX_BUSY is very suspicious.
> 
> I do not think a driver can implement xmit_more and keep
> NETDEV_TX_BUSY at the same time.
> 
> Please make sure to remove NETDEV_TX_BUSY first, by stopping the queue
> earlier.

Hi Eric, I think I understand your point and shall submit an updated patch. Thanks your time!