[dpdk-dev] [PATCH 1/5] vhost: refactor rte_vhost_dequeue_burst

[Stephen Hemminger]

On Thu,  3 Dec 2015 14:06:09 +0800
Yuanhan Liu <yuanhan.liu at linux.intel.com> wrote:

> +#define COPY(dst, src) do {						\
> +	cpy_len = RTE_MIN(desc_avail, mbuf_avail);			\
> +	rte_memcpy((void *)(uintptr_t)(dst),				\
> +		   (const void *)(uintptr_t)(src), cpy_len);		\
> +									\
> +	mbuf_avail  -= cpy_len;						\
> +	mbuf_offset += cpy_len;						\
> +	desc_avail  -= cpy_len;						\
> +	desc_offset += cpy_len;						\
> +} while(0)
> +

I see lots of issues here.

All those void * casts are unnecessary, C casts arguements already.
rte_memcpy is slower for constant size values than memcpy()

This macro violates the rule that ther should be no hidden variables
in a macro. I.e you are assuming cpy_len, desc_avail, and mbuf_avail
are defined in all code using the macro.

Why use an un-typed macro when an inline function would be just
as fast and give type safety?