netdev - Re: [PATCH net-next] net: mana: Add page pool for RX buffers

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Date: Fri, 14 Jul 2023 15:13:15 +0200
From: Jesper Dangaard Brouer <jbrouer@...hat.com>
To: Haiyang Zhang <haiyangz@...rosoft.com>,
 Jesper Dangaard Brouer <jbrouer@...hat.com>, Jakub Kicinski <kuba@...nel.org>
Cc: brouer@...hat.com,
 "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
 Dexuan Cui <decui@...rosoft.com>, KY Srinivasan <kys@...rosoft.com>,
 Paul Rosswurm <paulros@...rosoft.com>, "olaf@...fle.de" <olaf@...fle.de>,
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 Ilias Apalodimas <ilias.apalodimas@...aro.org>
Subject: Re: [PATCH net-next] net: mana: Add page pool for RX buffers



On 14/07/2023 14.51, Haiyang Zhang wrote:
> 
> 
>> -----Original Message-----
>> From: Jesper Dangaard Brouer <jbrouer@...hat.com>
>> On 14/07/2023 05.53, Jakub Kicinski wrote:
>>> On Thu, 13 Jul 2023 14:48:45 +0000 Haiyang Zhang wrote:
>>>> Add page pool for RX buffers for faster buffer cycle and reduce CPU
>>>> usage.
>>>>
>>>> Get an extra ref count of a page after allocation, so after upper
>>>> layers put the page, it's still referenced by the pool. We can reuse
>>>> it as RX buffer without alloc a new page.
>>>
>>> Please use the real page_pool API from include/net/page_pool.h
>>> We've moved past every driver reinventing the wheel, sorry.
>>
>> +1
>>
>> Quoting[1]: Documentation/networking/page_pool.rst
>>
>>    Basic use involves replacing alloc_pages() calls with the
>> page_pool_alloc_pages() call.
>>    Drivers should use page_pool_dev_alloc_pages() replacing
>> dev_alloc_pages().
>   
> Thank Jakub and Jesper for the reviews.
> I'm aware of the page_pool.rst doc, and actually tried it before this
> patch, but I got lower perf. If I understand correctly, we should call
> page_pool_release_page() before passing the SKB to napi_gro_receive().
> 
> I found the page_pool_dev_alloc_pages() goes through the slow path,
> because the page_pool_release_page() let the page leave the pool.
> 
> Do we have to call page_pool_release_page() before passing the SKB
> to napi_gro_receive()? Any better way to recycle the pages from the
> upper layer of non-XDP case?
> 

Today SKB "upper layers" can recycle page_pool backed packet data/page.

Just use skb_mark_for_recycle(skb), then you don't need 
page_pool_release_page().

I guess, we should update the documentation, mentioning this.

--Jesper