Hi, On 10/24/2016 05:49 PM, Morten Br?rup wrote: > And here?s something new to think about: > > m->next already reveals if there are more segments to a packet. Which > purpose does m->nb_segs serve that is not already covered by m->next? >
I was asking myself the same question some time ago: http://dpdk.org/ml/archives/dev/2016-May/039483.html But it seems nb_segs is useful for PMDs on TX side, to anticipate how many descriptors a packet will use in the TX ring. It can also help a PMD to check that this packet is supported by the hardware (too many segments) without browsing the list. So finally I think it should be kept in the mbuf. But as suggested by Bruce, it could go in the second cache line, since m->next is also there, at the condition that this field is set to 1 in mbuf_free(). Regards, Olivier
