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

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Message-ID: <bf070035-ba9c-d028-1b11-72af8651f979@huawei.com>
Date: Mon, 15 Apr 2024 21:19:45 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Alexander Duyck <alexander.duyck@...il.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 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?

> 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.