netdev - Re: [net-next PATCH 13/15] eth: fbnic: add basic Rx handling

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Message-ID: <CAKgT0UccovDVS8-TPXxgGbrTAqpeVHRQuCwf7f2qkfcPaPOA-A@mail.gmail.com>
Date: Mon, 15 Apr 2024 08:03:38 -0700
From: Alexander Duyck <alexander.duyck@...il.com>
To: Yunsheng Lin <linyunsheng@...wei.com>
Cc: netdev@...r.kernel.org, Alexander Duyck <alexanderduyck@...com>, kuba@...nel.org, 
	davem@...emloft.net, pabeni@...hat.com
Subject: Re: [net-next PATCH 13/15] eth: fbnic: add basic Rx handling

On Mon, Apr 15, 2024 at 6:19 AM Yunsheng Lin <linyunsheng@...wei.com> wrote:
>
> On 2024/4/12 23:05, Alexander Duyck wrote:
>
> ...
>
> >>
> >> From the below macro, this hw seems to be only able to handle 4K memory for
> >> each entry/desc in qt->sub0 and qt->sub1, so there seems to be a lot of memory
> >> that is unused for PAGE_SIZE > 4K as it is allocating memory based on page
> >> granularity for each rx_buf in qt->sub0 and qt->sub1.
> >>
> >> +#define FBNIC_RCD_AL_BUFF_OFF_MASK             DESC_GENMASK(43, 32)
> >
> > The advantage of being a purpose built driver is that we aren't
> > running on any architectures where the PAGE_SIZE > 4K. If it came to
>
> I am not sure if 'being a purpose built driver' argument is strong enough
> here, at least the Kconfig does not seems to be suggesting it is a purpose
> built driver, perhaps add a 'depend on' to suggest that?

I'm not sure if you have been following the other threads. One of the
general thoughts of pushback against this driver was that Meta is
currently the only company that will have possession of this NIC. As
such Meta will be deciding what systems it goes into and as a result
of that we aren't likely to be running it on systems with 64K pages.

> > that we could probably look at splitting the pages within the
> > descriptors by simply having a single page span multiple descriptors.
>
> My point is that we might be able to meet the above use case with a proper
> API without driver manipulating the reference counting by calling
> page_pool_fragment_page() directly.

My suggestion would be to look at putting your proposed API together
as something that can be used by another driver. Once we hit that I
can then look at incorporating it into fbnic. One issue right now is
that the current patch set is meant to make use of existing APIs
instead of needing to rely on creating new ones as this isn't a device
others will have access to so it will make it harder to test any
proposed API based only on fbnic.