[dpdk-dev] [PATCH 1/1] net/af_xdp: shared UMEM support

[Loftus, Ciara]

> >
> > Kernel v5.10 will introduce the ability to efficiently share a UMEM between
> > AF_XDP sockets bound to different queue ids on the same or different
> > devices. This patch integrates that functionality into the AF_XDP PMD.
> >
> > A PMD will attempt to share a UMEM with others if the shared_umem=1
> > vdev arg is set. UMEMs can only be shared across PMDs with the same
> > mempool, up to a limited number of PMDs goverened by the size of the
> > given mempool.
> > Sharing UMEMs is not supported for non-zero-copy (aligned) mode.
> >
> > The benefit of sharing UMEM across PMDs is a saving in memory due to not
> > having to register the UMEM multiple times. Throughput was measured to
> > remain within 2% of the default mode (not sharing UMEM).
> >
> > A version of libbpf >= v0.2.0 is required and the appropriate pkg-config file
> > for libbpf must be installed such that meson can determine the version.
> >
> > Signed-off-by: Ciara Loftus <ciara.loftus at intel.com>
> 
> <snip>
> 
> >
> > +/* List which tracks PMDs to facilitate sharing UMEMs across them. */
> > +struct internal_list {
> > +TAILQ_ENTRY(internal_list) next;
> > +struct rte_eth_dev *eth_dev;
> > +};
> > +
> > +TAILQ_HEAD(internal_list_head, internal_list); static struct
> > +internal_list_head internal_list =
> > +TAILQ_HEAD_INITIALIZER(internal_list);
> > +
> > +static pthread_mutex_t internal_list_lock =
> PTHREAD_MUTEX_INITIALIZER;
> 
> [Tahhan, Maryam] do multiple threads typically initialize and ethdev/invoke
> the underlying driver?
> Most apps I've seen initialize the ports one after the other in the starting
> thread - so if there's not multiple threads doing initialization - we may want
> to consider removing this mutex...
> Or maybe do you see something potentially removing a port while a port is
> being added?

Hi Maryam,

Yes. Although unlikely, I'm not aware of any guarantee that a port A cannot be removed when port B is being added and since both operations can touch the tailq I'm inclined to keep the mutex. But I'm open to correction.

Thanks,
Ciara

> 
> <snip>