Hi Bruce,
On 08/11/2014 10:44 PM, Bruce Richardson wrote:
> From: Olivier Matz <olivier.matz at 6wind.com>
>
> Original patch:
> The mbuf structure already contains a pointer to the beginning of the
> buffer (m->buf_addr). It is not needed to use 8 bytes again to store
> another pointer to the beginning of the data.
>
> Using a 16 bits unsigned integer is enough as we know that a mbuf is
> never longer than 64KB. We gain 6 bytes in the structure thanks to
> this modification.
>
> Signed-off-by: Olivier Matz <olivier.matz at 6wind.com>
>
> This version:
> * Updated original patch to apply to latest on mainline.
> * Disabled vector PMD in config as it relies heavily on the mbuf layout
>
> Signed-off-by: Bruce Richardson <bruce.richardson at intel.com>
Remaining references shown by:
git grep
"\(pkt->data[^_]\)\|\(mb->data[^_]\)\|\(m->data[^_]\)\|\(mbuf->data[^_]\)"
In:
app/test-pmd/ieee1588fwd.c
examples/vhost_xen/main.c
lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
lib/librte_pmd_pcap/rte_eth_pcap.c
lib/librte_pmd_xenvirt/rte_eth_xenvirt.c
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -140,6 +140,13 @@ struct rte_mbuf {
> void *buf_addr; /**< Virtual address of segment buffer. */
> phys_addr_t buf_physaddr; /**< Physical address of segment buffer. */
> uint16_t buf_len; /**< Length of segment buffer. */
> +
> + /* valid for any segment */
> + struct rte_mbuf *next; /**< Next segment of scattered packet. */
> + uint16_t data_off;
> + uint16_t data_len; /**< Amount of data in segment buffer. */
> + uint32_t pkt_len; /**< Total pkt len: sum of all segments. */
> +
> #ifdef RTE_MBUF_REFCNT
> /**
> * 16-bit Reference counter.
> @@ -156,18 +163,12 @@ struct rte_mbuf {
> #else
> uint16_t refcnt_reserved; /**< Do not use this field */
> #endif
> - uint16_t reserved; /**< Unused field. Required for padding.
> */
> - uint16_t ol_flags; /**< Offload features. */
> -
> - /* valid for any segment */
> - struct rte_mbuf *next; /**< Next segment of scattered packet. */
> - void* data; /**< Start address of data in segment buffer. */
> - uint16_t data_len; /**< Amount of data in segment buffer. */
>
> /* these fields are valid for first segment only */
> uint8_t nb_segs; /**< Number of segments. */
> uint8_t in_port; /**< Input port. */
> - uint32_t pkt_len; /**< Total pkt len: sum of all segment
> data_len. */
> + uint16_t ol_flags; /**< Offload features. */
> + uint16_t reserved; /**< Unused field. Required for padding.
> */
I think we should try to keep comments aligned if possible.
>
> /* offload features, valid for first segment only */
> union rte_vlan_macip vlan_macip;
> @@ -185,7 +186,7 @@ struct rte_mbuf {
> uint16_t metadata16[0];
> uint32_t metadata32[0];
> uint64_t metadata64[0];
> - };
> + } __rte_cache_aligned;
> } __rte_cache_aligned;
>
In my initial patch, there was a "reserved2" field at the end of the
rte_mbuf structure to keep its size to 64 bytes. This is not really
required because of the __rte_cache_aligned, but I wonder if it's a
problem to have metadata not starting on a cache line. There can be
some conflicts if some part of the code use *(uint32 *)(m + 1)
and other part of code m->metadata32[0].
By the way (that's completely off-topic), but I don't really see why
having this metadata at the end of mbuf structure is useful.
> @@ -1523,7 +1523,8 @@ ixgbe_recv_scattered_pkts(void *rx_queue, struct
> rte_mbuf **rx_pkts,
> }
>
> /* Prefetch data of first segment, if configured to do so. */
> - rte_packet_prefetch(first_seg->data);
> + rte_packet_prefetch((char *)first_seg->buf_addr +
> + first_seg->data_off);
>
It seems there is a trailing whitespace here after the "+" (seen by
"git am").
Regards,
Olivier
