Dear Team
I would like bring it to your kind notice of below code of vpp-1707-dpdk
plunging.
static_always_inline void dpdk_prefetch_buffer_by_index (vlib_main_t * vm, u32
bi)
{
vlib_buffer_t *b;
struct rte_mbuf *mb;
b = vlib_get_buffer (vm, bi);
mb = rte_mbuf_from_vlib_buffer (b);
CLIB_PREFETCH (mb, CLIB_CACHE_LINE_BYTES, LOAD);
CLIB_PREFETCH (b, CLIB_CACHE_LINE_BYTES, LOAD);
}
#define CLIB_PREFETCH(addr,size,type) \
do { \
void * _addr = (addr); \
\
ASSERT ((size) <= 4*CLIB_CACHE_LINE_BYTES); \
_CLIB_PREFETCH (0, size, type); \
_CLIB_PREFETCH (1, size, type); \
_CLIB_PREFETCH (2, size, type); \
_CLIB_PREFETCH (3, size, type); \
} while (0)
[cid:a4244621-4b4e-4fe0-b6e7-c6928cd4909a]
Here , Sizeof(rte_mbuf) = 128 and sizeof(vlib_buffer_t) = 128 + HEAD_ROOM(128)=
256.
In above code part, vlib_buffer is ahead of 128 bytes from start of rte_mbuf
structure. As i understood one CLIB_PREFETCH will load 256 bytes from memory.
,hence total pre-fetch is 512 bytes. As per the above code first CLIB_PREFETCH
will load 256, which includes 128 of rte_mbuf + 128 of vlib_buffer as well .
2nd CLIB_PREFETCH will also load vlib_buffer whcih as ready has been loaded.
I must say duplication in prefetching the memory. Please correct me if I am
wrong.
Regards
MJ
Senior Project Engineer.
Mob: 9735128504
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