[dpdk-dev] [PATCH 4/5] mbuf: add userdata pointer field
Neil Horman
nhorman at tuxdriver.com
Wed Sep 17 17:35:10 CEST 2014
On Wed, Sep 17, 2014 at 11:01:41AM +0100, Bruce Richardson wrote:
> While some applications may store metadata about packets in the packet
> mbuf headroom, this is not a workable solution for packet metadata which
> is either:
> * larger than the headroom (or headroom is needed for adding pkt headers)
> * needs to be shared or copied among packets
>
> To support these use cases in applications, we reserve a general
> "userdata" pointer field inside the second cache-line of the mbuf. This
> is better than having the application store the pointer to the external
> metadata in the packet headroom, as it saves an additional cache-line
> from being used.
>
> Apart from storing metadata, this field also provides a general 8-byte
> scratch space inside the mbuf for any other application uses that are
> applicable.
>
> Signed-off-by: Bruce Richardson <bruce.richardson at intel.com>
> ---
> lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h | 3 ++-
> lib/librte_mbuf/rte_mbuf.h | 3 +++
> 2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h b/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
> index 25ed672..d27e891 100644
> --- a/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
> +++ b/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
> @@ -117,7 +117,8 @@ struct rte_kni_mbuf {
> uint16_t data_len; /**< Amount of data in segment buffer. */
> uint32_t pkt_len; /**< Total pkt len: sum of all segment data_len. */
> char pad3[8];
> - void *pool __attribute__((__aligned__(64)));
> + void *pad4 __attribute__((__aligned__(64)));
> + void *pool;
I don't see a comment about this in the changelog, only about the userdata
pointer being added below.
> void *next;
> };
>
> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> index 8e27d2e..b1acfc3 100644
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -172,6 +172,9 @@ struct rte_mbuf {
>
> /* second cache line - fields only used in slow path or on TX */
> MARKER cacheline1 __rte_cache_aligned;
> +
> + void *userdata; /**< Can be used for external metadata */
> +
Do you want to make this a void* or a char[8]? I ask because if people are
going to use is as a scratch space (rather than a pointer), they get a suprise
when they build this on 32 bit systems, and their 8 byte scratch space is
reduced to 4 bytes.
Neil
> struct rte_mempool *pool; /**< Pool from which mbuf was allocated. */
> struct rte_mbuf *next; /**< Next segment of scattered packet. */
>
> --
> 1.9.3
>
>
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