On 10/30/20 8:29 PM, Thomas Monjalon wrote:
The mempool pointer in the mbuf struct is moved
from the second to the first half.
It should increase performance on most systems having 64-byte cache line,
i.e. mbuf is split in two cache lines.
On such system, the first half (also called first cache line) is hotter
than the second one where the pool pointer was.
Moving this field gives more space to dynfield1.
This is how the mbuf layout looks like (pahole-style):
word type name byte size
0 void * buf_addr; /* 0 + 8 */
1 rte_iova_t buf_iova /* 8 + 8 */
/* --- RTE_MARKER64 rearm_data; */
2 uint16_t data_off; /* 16 + 2 */
uint16_t refcnt; /* 18 + 2 */
uint16_t nb_segs; /* 20 + 2 */
uint16_t port; /* 22 + 2 */
3 uint64_t ol_flags; /* 24 + 8 */
/* --- RTE_MARKER rx_descriptor_fields1; */
4 uint32_t union packet_type; /* 32 + 4 */
uint32_t pkt_len; /* 36 + 4 */
5 uint16_t data_len; /* 40 + 2 */
uint16_t vlan_tci; /* 42 + 2 */
5.5 uint64_t union hash; /* 44 + 8 */
6.5 uint16_t vlan_tci_outer; /* 52 + 2 */
uint16_t buf_len; /* 54 + 2 */
7 struct rte_mempool * pool; /* 56 + 8 */
/* --- RTE_MARKER cacheline1; */
8 struct rte_mbuf * next; /* 64 + 8 */
9 uint64_t union tx_offload; /* 72 + 8 */
10 uint16_t priv_size; /* 80 + 2 */
uint16_t timesync; /* 82 + 2 */
uint32_t seqn; /* 84 + 4 */
As I understand rebase is required since seqn is already removed
(or at least fix here).
11 struct rte_mbuf_ext_shared_info * shinfo; /* 88 + 8 */
12 uint64_t dynfield1[4]; /* 96 + 32 */
16 /* --- END 128 */
Signed-off-by: Thomas Monjalon <tho...@monjalon.net>
Taking Konstantin reply into account ('next' is used on free in any case
together
with 'pool', so the second cache line is accessed in any case), I think
that 'next' is
a better candidate. Also 'tx_offload' is a better candidate than 'pool'.
I think 'next' is better since it works for both Rx and Tx, but
'tx_offload' is Tx only.
