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 > >