Re: [dpdk-dev] [PATCH v2 1/2] mbuf: provide rte_pktmbuf_alloc_bulk API

["Xie, Huawei" <huawei.xie@intel.com>]

On 12/18/2015 1:03 PM, Stephen Hemminger wrote:
> On Mon, 14 Dec 2015 09:14:41 +0800
> Huawei Xie <huawei.xie@intel.com> wrote:
>
>> v2 changes:
>>  unroll the loop a bit to help the performance
>>
>> rte_pktmbuf_alloc_bulk allocates a bulk of packet mbufs.
>>
>> There is related thread about this bulk API.
>> http://dpdk.org/dev/patchwork/patch/4718/
>> Thanks to Konstantin's loop unrolling.
>>
>> Signed-off-by: Gerald Rogers <gerald.rogers@intel.com>
>> Signed-off-by: Huawei Xie <huawei.xie@intel.com>
>> Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
>> ---
>>  lib/librte_mbuf/rte_mbuf.h | 50 ++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 50 insertions(+)
>>
>> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
>> index f234ac9..4e209e0 100644
>> --- a/lib/librte_mbuf/rte_mbuf.h
>> +++ b/lib/librte_mbuf/rte_mbuf.h
>> @@ -1336,6 +1336,56 @@ static inline struct rte_mbuf *rte_pktmbuf_alloc(struct rte_mempool *mp)
>>  }
>>  
>>  /**
>> + * Allocate a bulk of mbufs, initialize refcnt and reset the fields to default
>> + * values.
>> + *
>> + *  @param pool
>> + *    The mempool from which mbufs are allocated.
>> + *  @param mbufs
>> + *    Array of pointers to mbufs
>> + *  @param count
>> + *    Array size
>> + *  @return
>> + *   - 0: Success
>> + */
>> +static inline int rte_pktmbuf_alloc_bulk(struct rte_mempool *pool,
>> +	 struct rte_mbuf **mbufs, unsigned count)
>> +{
>> +	unsigned idx = 0;
>> +	int rc;
>> +
>> +	rc = rte_mempool_get_bulk(pool, (void **)mbufs, count);
>> +	if (unlikely(rc))
>> +		return rc;
>> +
>> +	switch (count % 4) {
>> +	while (idx != count) {
>> +		case 0:
>> +			RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 0);
>> +			rte_mbuf_refcnt_set(mbufs[idx], 1);
>> +			rte_pktmbuf_reset(mbufs[idx]);
>> +			idx++;
>> +		case 3:
>> +			RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 0);
>> +			rte_mbuf_refcnt_set(mbufs[idx], 1);
>> +			rte_pktmbuf_reset(mbufs[idx]);
>> +			idx++;
>> +		case 2:
>> +			RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 0);
>> +			rte_mbuf_refcnt_set(mbufs[idx], 1);
>> +			rte_pktmbuf_reset(mbufs[idx]);
>> +			idx++;
>> +		case 1:
>> +			RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 0);
>> +			rte_mbuf_refcnt_set(mbufs[idx], 1);
>> +			rte_pktmbuf_reset(mbufs[idx]);
>> +			idx++;
>> +	}
>> +	}
>> +	return 0;
>> +}
> This is weird. Why not just use Duff's device in a more normal manner.
Hi Stephen: I just compared with duff's unrolled version. It is slightly
different, but where is weird?
>
>