Re: [dpdk-dev] [RFC PATCH] ixgbe: ixgbe_recv_pkts_vec shouldn't override mbuf buffer length

[Jean-Mickael Guerin <jean-mickael.guerin@6wind.com>]

On 05/12/2014 18:07, Ananyev, Konstantin wrote:
>
>
>> -----Original Message-----
>> From: Jean-Mickael Guerin [mailto:jean-mickael.guerin@6wind.com]
>> Sent: Friday, December 05, 2014 4:59 PM
>> To: Ananyev, Konstantin
>> Cc: dev@dpdk.org
>> Subject: Re: [dpdk-dev] [RFC PATCH] ixgbe: ixgbe_recv_pkts_vec shouldn't override mbuf buffer length
>>
>> On 05/12/2014 16:20, Konstantin Ananyev wrote:
>>> That's an alternative way to fix the problem described in the patch:
>>> http://dpdk.org/ml/archives/dev/2014-December/009394.html.
>>> The main difference is:
>>> - move buf_len fields out of rearm_data marker.
>>> - make ixgbe_recv_pkts_vec() not touch buf_len field at all
>>> (as all other RX functions behave).
>>>
>>> Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
>>> ---
>>>    lib/librte_mbuf/rte_mbuf.h            |  7 +++++--
>>>    lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c | 20 +++++++++++++++-----
>>>    2 files changed, 20 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
>>> index 2e5fce5..bb88318 100644
>>> --- a/lib/librte_mbuf/rte_mbuf.h
>>> +++ b/lib/librte_mbuf/rte_mbuf.h
>>> @@ -179,6 +179,8 @@ const char *rte_get_tx_ol_flag_name(uint64_t mask);
>>>    typedef void    *MARKER[0];   /**< generic marker for a point in a structure */
>>>    typedef uint64_t MARKER64[0]; /**< marker that allows us to overwrite 8 bytes
>>>                                   * with a single assignment */
>>> +typedef uint8_t MARKER8[0];   /**< generic marker with 1B alignment */
>>> +
>>>    /**
>>>     * The generic rte_mbuf, containing a packet mbuf.
>>>     */
>>> @@ -188,9 +190,10 @@ struct rte_mbuf {
>>>    	void *buf_addr;           /**< Virtual address of segment buffer. */
>>>    	phys_addr_t buf_physaddr; /**< Physical address of segment buffer. */
>>>
>>> -	/* next 8 bytes are initialised on RX descriptor rearm */
>>> -	MARKER64 rearm_data;
>>>    	uint16_t buf_len;         /**< Length of segment buffer. */
>>> +
>>> +	/* next 6 bytes are initialised on RX descriptor rearm */
>>> +	MARKER8 rearm_data;
>>>    	uint16_t data_off;
>>>
>>>    	/**
>>> diff --git a/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c b/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
>>> index 579bc46..d5fc0cc 100644
>>> --- a/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
>>> +++ b/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
>>> @@ -79,13 +79,22 @@ ixgbe_rxq_rearm(struct igb_rx_queue *rxq)
>>>    	/* Initialize the mbufs in vector, process 2 mbufs in one loop */
>>>    	for (i = 0; i < RTE_IXGBE_RXQ_REARM_THRESH; i += 2, rxep += 2) {
>>>    		__m128i vaddr0, vaddr1;
>>> +		uintptr_t p0, p1;
>>>
>>>    		mb0 = rxep[0].mbuf;
>>>    		mb1 = rxep[1].mbuf;
>>>
>>> -		/* flush mbuf with pkt template */
>>> -		mb0->rearm_data[0] = rxq->mbuf_initializer;
>>> -		mb1->rearm_data[0] = rxq->mbuf_initializer;
>>> +		/*
>>> +		 * Flush mbuf with pkt template.
>>> +		 * Data to be rearmed is 6 bytes long.
>>> +		 * Though, RX will overwrite ol_flags that are coming next
>>> +		 * anyway. So overwrite whole 8 bytes with one load:
>>> +		 * 6 bytes of rearm_data plus first 2 bytes of ol_flags.
>>> +		 */
>>> +		p0 = (uintptr_t)&mb0->rearm_data;
>>> +		*(uint64_t *)p0 = rxq->mbuf_initializer;
>>> +		p1 = (uintptr_t)&mb1->rearm_data;
>>> +		*(uint64_t *)p1 = rxq->mbuf_initializer;
>>>
>>>    		/* load buf_addr(lo 64bit) and buf_physaddr(hi 64bit) */
>>>    		vaddr0 = _mm_loadu_si128((__m128i *)&(mb0->buf_addr));
>>> @@ -732,14 +741,15 @@ static struct ixgbe_txq_ops vec_txq_ops = {
>>>    int
>>>    ixgbe_rxq_vec_setup(struct igb_rx_queue *rxq)
>>>    {
>>> +	uintptr_t p;
>>>    	struct rte_mbuf mb_def = { .buf_addr = 0 }; /* zeroed mbuf */
>>>
>>>    	mb_def.nb_segs = 1;
>>>    	mb_def.data_off = RTE_PKTMBUF_HEADROOM;
>>> -	mb_def.buf_len = rxq->mb_pool->elt_size - sizeof(struct rte_mbuf);
>>>    	mb_def.port = rxq->port_id;
>>>    	rte_mbuf_refcnt_set(&mb_def, 1);
>>> -	rxq->mbuf_initializer = *((uint64_t *)&mb_def.rearm_data);
>>> +	p = (uintptr_t)&mb_def.rearm_data;
>>> +	rxq->mbuf_initializer = *(uint64_t *)p;
>>>    	return 0;
>>>    }
>>>
>>>
>>
>> The patch introduces writes on unaligned data, but we can assume no
>> performance penalty on intel hw, correct?
>>
>
> Yes to both:
> it introduces 64bit unaligned store.
> I run performance test on IVB board, didn't see any degradation.
> Konstantin
>
>
OK fine by me:

Acked-by: Jean-Mickael Guerin <jean-mickael.guerin@6wind.com>