Re: [dpdk-dev] [PATCH v1 1/3] ixgbe: Use the rte_le_to_cpu_xx()/rte_cpu_to_le_xx() when reading/setting HW ring descriptor fields

[Vlad Zolotarov <vladz@cloudius-systems.com>]

On 03/09/15 12:29, Ananyev, Konstantin wrote:
> Hi Vlad,
>
>> -----Original Message-----
>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Vlad Zolotarov
>> Sent: Monday, March 09, 2015 10:13 AM
>> To: dev@dpdk.org
>> Subject: [dpdk-dev] [PATCH v1 1/3] ixgbe: Use the rte_le_to_cpu_xx()/rte_cpu_to_le_xx() when reading/setting HW ring descriptor
>> fields
>>
>> Fixed the above in ixgbe_rx_alloc_bufs() and in ixgbe_recv_scattered_pkts().
>>
>> Signed-off-by: Vlad Zolotarov <vladz@cloudius-systems.com>
>> ---
>>   lib/librte_pmd_ixgbe/ixgbe_rxtx.c | 13 +++++++------
>>   1 file changed, 7 insertions(+), 6 deletions(-)
>>
>> diff --git a/lib/librte_pmd_ixgbe/ixgbe_rxtx.c b/lib/librte_pmd_ixgbe/ixgbe_rxtx.c
>> index 9ecf3e5..b033e04 100644
>> --- a/lib/librte_pmd_ixgbe/ixgbe_rxtx.c
>> +++ b/lib/librte_pmd_ixgbe/ixgbe_rxtx.c
>> @@ -1028,7 +1028,7 @@ ixgbe_rx_alloc_bufs(struct igb_rx_queue *rxq)
>>   	struct igb_rx_entry *rxep;
>>   	struct rte_mbuf *mb;
>>   	uint16_t alloc_idx;
>> -	uint64_t dma_addr;
>> +	__le64 dma_addr;
> Wonder Why you changed from uint64_t to __le64 here?
> Effectively __le64 is the same a uint64_t,

I'm afraid the above it's not completely correct. See below.

> and I think it is better to use always the same type across all PMD code for consistency.

Pls., note that "dma_addr" is only used (see below)...

> Konstantin
>
>
>>   	int diag, i;
>>
>>   	/* allocate buffers in bulk directly into the S/W ring */
>> @@ -1051,7 +1051,7 @@ ixgbe_rx_alloc_bufs(struct igb_rx_queue *rxq)
>>   		mb->port = rxq->port_id;
>>
>>   		/* populate the descriptors */
>> -		dma_addr = (uint64_t)mb->buf_physaddr + RTE_PKTMBUF_HEADROOM;
>> +		dma_addr = rte_cpu_to_le_64(RTE_MBUF_DATA_DMA_ADDR_DEFAULT(mb));
>>   		rxdp[i].read.hdr_addr = dma_addr;
>>   		rxdp[i].read.pkt_addr = dma_addr;

here. ;) And the type of both hdr_addr and pkt_addr is __le64.
I don't exactly understand what do u mean by "use the same type across 
all PMD code for consistency" - there are a lot of types used in the PMD 
code and __le64 is one of them... ;)

Now more seriously, let's recall what is the semantics of the __leXX 
types - they represent the integer in the "little endian" format. Here, 
NIC expects the physical address in a little endian format, thus the 
descriptor is defined the way it is defined - using __le64. The same 
relates to dma_addr local variable in this patch - it contains the 
physical (more correctly "DMA-able") address of the Rx buffer in the 
form NIC expects it to be written in the descriptor.

So, why to use __leXX anyway? - Debugging the (invalid) endianess is a 
real headache. Therefore there are a few static code analysis tools like 
"sparse" that allow to detect such inconsistencies (see here 
http://en.wikipedia.org/wiki/Sparse) and __leXX is a helper to allow 
tools like sparse to detect such problems.

In addition after spending some time writing patches for Linux netdev 
list u develop a strong habit for such stuff - Dave and others are very 
strict about such things... ;)

So, is it the same as uint64_t? I guess now it's clear why it is now... ;)

>>   	}
>> @@ -1559,13 +1559,14 @@ ixgbe_recv_scattered_pkts(void *rx_queue, struct rte_mbuf **rx_pkts,
>>   		first_seg->ol_flags = pkt_flags;
>>
>>   		if (likely(pkt_flags & PKT_RX_RSS_HASH))
>> -			first_seg->hash.rss = rxd.wb.lower.hi_dword.rss;
>> +			first_seg->hash.rss =
>> +				    rte_le_to_cpu_32(rxd.wb.lower.hi_dword.rss);
>>   		else if (pkt_flags & PKT_RX_FDIR) {
>>   			first_seg->hash.fdir.hash =
>> -				(uint16_t)((rxd.wb.lower.hi_dword.csum_ip.csum)
>> -					   & IXGBE_ATR_HASH_MASK);
>> +			    rte_le_to_cpu_16(rxd.wb.lower.hi_dword.csum_ip.csum)
>> +					   & IXGBE_ATR_HASH_MASK;
>>   			first_seg->hash.fdir.id =
>> -				rxd.wb.lower.hi_dword.csum_ip.ip_id;
>> +			  rte_le_to_cpu_16(rxd.wb.lower.hi_dword.csum_ip.ip_id);
>>   		}
>>
>>   		/* Prefetch data of first segment, if configured to do so. */
>> --
>> 2.1.0