linux-kernel - Re: [PATCH net-next 2/2] page_pool: optimize the cpu sync operation when DMA mapping

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Date:   Fri, 20 Aug 2021 14:29:46 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Heiner Kallweit <hkallweit1@...il.com>, <davem@...emloft.net>,
        <kuba@...nel.org>
CC:     <hawk@...nel.org>, <ilias.apalodimas@...aro.org>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 2/2] page_pool: optimize the cpu sync operation
 when DMA mapping

On 2021/8/20 14:10, Heiner Kallweit wrote:
> On 20.08.2021 04:06, Yunsheng Lin wrote:
>> If the DMA_ATTR_SKIP_CPU_SYNC is not set, cpu syncing is
>> also done in dma_map_page_attrs(), so set the attrs according
>> to pool->p.flags to avoid calling dma sync function again.
>>
>> Also mark the dma error as the unlikely case While we are at
>> it.
>>
> This shouldn't be needed. dma_mapping_error() will be (most likely)
> inlined by the compiler, and it includes the unlikely() hint.

Good point, will remove the unlikely() mark.
Thanks.

> 
>> Signed-off-by: Yunsheng Lin <linyunsheng@...wei.com>
>> ---
>>  net/core/page_pool.c | 11 ++++++-----
>>  1 file changed, 6 insertions(+), 5 deletions(-)
>>
>> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
>> index 1a69784..8172045 100644
>> --- a/net/core/page_pool.c
>> +++ b/net/core/page_pool.c
>> @@ -191,8 +191,12 @@ static void page_pool_dma_sync_for_device(struct page_pool *pool,
>>  
>>  static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
>>  {
>> +	unsigned long attrs = DMA_ATTR_SKIP_CPU_SYNC;
>>  	dma_addr_t dma;
>>  
>> +	if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
>> +		attrs = 0;
>> +
>>  	/* Setup DMA mapping: use 'struct page' area for storing DMA-addr
>>  	 * since dma_addr_t can be either 32 or 64 bits and does not always fit
>>  	 * into page private data (i.e 32bit cpu with 64bit DMA caps)
>> @@ -200,15 +204,12 @@ static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
>>  	 */
>>  	dma = dma_map_page_attrs(pool->p.dev, page, 0,
>>  				 (PAGE_SIZE << pool->p.order),
>> -				 pool->p.dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
>> -	if (dma_mapping_error(pool->p.dev, dma))
>> +				 pool->p.dma_dir, attrs);
>> +	if (unlikely(dma_mapping_error(pool->p.dev, dma)))
>>  		return false;
>>  
>>  	page_pool_set_dma_addr(page, dma);
>>  
>> -	if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
>> -		page_pool_dma_sync_for_device(pool, page, pool->p.max_len);
>> -
>>  	return true;
>>  }
>>  
>>
> 
> .
>