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

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

On Mon, Dec 14, 2015 at 09:14:41AM +0800, Huawei Xie 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)

It violates the coding style a bit.

> +{
> +	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) {

Well, that's an awkward trick, putting while between switch and case.

How about moving the whole switch block ahead, and use goto?

	switch (count % 4) {
	case 3:
		goto __3;
		break;
	case 2:
		goto __2;
		break;
	...

	}

It basically generates same instructions, yet it improves the
readability a bit.

	--yliu

> +		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;
> +}
> +
> +/**
>   * Attach packet mbuf to another packet mbuf.
>   *
>   * After attachment we refer the mbuf we attached as 'indirect',
> -- 
> 1.8.1.4