netdev - Re: [PATCH v5 10/17] net: sgi: ioc3-eth: rework skb rx handling

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Date:   Wed, 21 Aug 2019 13:37:57 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Thomas Bogendoerfer <tbogendoerfer@...e.de>
Cc:     Jonathan Corbet <corbet@....net>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        "David S. Miller" <davem@...emloft.net>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Evgeniy Polyakov <zbr@...emap.net>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-input@...r.kernel.org, netdev@...r.kernel.org,
        linux-rtc@...r.kernel.org, linux-serial@...r.kernel.org,
        Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH v5 10/17] net: sgi: ioc3-eth: rework skb rx handling

On Wed, 21 Aug 2019 16:28:47 +0200, Thomas Bogendoerfer wrote:
> > This looks like a DMA engine alignment requirement, more than an
> > optimization.  
> 
> that true, there are two constraints for the rx buffers, start must be aligned
> to 128 bytes and a buffer must not cross a 16kbyte boundary. I was already
> thinking of allocating pages and chop them up. Is there a Linux API available,
> which could help for implementing this ?
> 
> I'll probably drop this patch or only change the skb_put stuff plus RX_BUF_SIZE
> define.

Sounds a little like frag allocator (napi_alloc_frag()/
netdev_alloc_frag()), but I'm not sure you'd have sufficient control
to skip over the 16k boundary.. Perhaps others have better suggestions.