linux-kernel - Re: [PATCH net-next v2] octeontx2-pf: Add support for page pool

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Message-ID: <0136fe46-eeb7-782d-0616-2a444e2f2da4@huawei.com>
Date:   Fri, 19 May 2023 10:37:00 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Ratheesh Kannoth <rkannoth@...vell.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Sunil Kovvuri Goutham <sgoutham@...vell.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        Subbaraya Sundeep Bhatta <sbhatta@...vell.com>,
        Geethasowjanya Akula <gakula@...vell.com>,
        Srujana Challa <schalla@...vell.com>,
        Hariprasad Kelam <hkelam@...vell.com>
Subject: Re: [PATCH net-next v2] octeontx2-pf: Add support for page pool

On 2023/5/19 9:52, Ratheesh Kannoth wrote:
>> ----------------------------------------------------------------------
>> On 2023/5/18 13:51, Ratheesh Kannoth wrote:
>>> Page pool for each rx queue enhance rx side performance by reclaiming
>>> buffers back to each queue specific pool. DMA mapping is done only for
>>> first allocation of buffers.
>>> As subsequent buffers allocation avoid DMA mapping, it results in
>>> performance improvement.
>>>
>>> Image        |  Performance with Linux kernel Packet Generator
>>
>> Is there any more detailed info for the performance data?
>> 'kernel Packet Generator' means using pktgen module in the
>> net/core/pktgen.c? it seems pktgen is more for tx, is there any abvious
>> reason why the page pool optimization for rx have brought about ten times
>> improvement?
> We used packet generator for TX machine.  Performance data is for RX DUT.  I will remove 
> Packet generator text from the commit message as it gives ambiguous information
> DUT  Rx     <-------------------------     TX  (Linux machine with packet generator)
>  (page pool support) 

Thanks for clarifying.
DUT is for 'Device Under Test'?
what does DUT do after it receive a packet? XDP DROP?

> 
>>
>>> ------------ | -----------------------------------------------
>>> Vannila      |   3Mpps
>>>              |
>>> with this    |   42Mpps
>>> change	     |
>>> -------------------------------------------------------------
>>>
>>
>> ...
>>
>>>  static int __otx2_alloc_rbuf(struct otx2_nic *pfvf, struct otx2_pool *pool,
>>>  			     dma_addr_t *dma)
>>>  {
>>>  	u8 *buf;
>>>
>>> +	if (pool->page_pool)
>>> +		return otx2_alloc_pool_buf(pfvf, pool, dma);
>>> +
>>>  	buf = napi_alloc_frag_align(pool->rbsize, OTX2_ALIGN);
>>>  	if (unlikely(!buf))
>>>  		return -ENOMEM;
>>
>> It seems the above is dead code when using 'select PAGE_POOL', as
>> PAGE_POOL config is always selected by the driver?
> _otx2_alloc_rbuf() is common code for RX and TX.  For RX,  pool->page_pool != NULL, so allocation is from page pool.
> 

Am I missing something here? 'buf' is dma-mapped with
DMA_FROM_DEVICE, can it be used for TX?

Also, what does 'r' in _otx2_alloc_rbuf() mean?