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

["Loftus, Ciara" <ciara.loftus@intel.com>]

> 
> On 8/11/2020 10:50 AM, Ciara Loftus wrote:
> > A future kernel 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.
> >
> > The benefit of sharing UMEM across PMDs is a saving in memory due to not
> > having to register the UMEM multiple times.
> >
> > Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>
> 
> <...>
> 
> > @@ -1,5 +1,5 @@
> >  /* SPDX-License-Identifier: BSD-3-Clause
> > - * Copyright(c) 2019 Intel Corporation.
> > + * Copyright(c) 2020 Intel Corporation.
> >   */
> >  #include <unistd.h>
> >  #include <errno.h>
> > @@ -15,6 +15,7 @@
> >  #include <linux/if_link.h>
> >  #include <linux/ethtool.h>
> >  #include <linux/sockios.h>
> > +#include <linux/version.h>
> >  #include "af_xdp_deps.h"
> >  #include <bpf/xsk.h>
> >
> > @@ -37,6 +38,11 @@
> >  #include <rte_mbuf.h>
> >  #include <rte_malloc.h>
> >  #include <rte_ring.h>
> > +#include <rte_spinlock.h>
> > +
> > +#if KERNEL_VERSION(5, 7, 0) < LINUX_VERSION_CODE
> > +#define ETH_AF_XDP_SHARED_UMEM 1
> > +#endif
> 
> I think better to separate these version checks from the actual code, what do
> you think creating a compat.h under 'net/af_xdp' and move above logic
> there?

Good suggestion. Much cleaner. I'll implement this.

> 
> <...>
> 
> > @@ -888,9 +1048,15 @@ xsk_configure(struct pmd_internals *internals,
> struct pkt_rx_queue *rxq,
> >  	cfg.bind_flags |= XDP_USE_NEED_WAKEUP;
> >  #endif
> >
> > -	ret = xsk_socket__create(&rxq->xsk, internals->if_name,
> > -			rxq->xsk_queue_idx, rxq->umem->umem, &rxq->rx,
> > -			&txq->tx, &cfg);
> > +	if (!internals->shared_umem_configured) {
> > +		ret = xsk_socket__create(&rxq->xsk, internals->if_name,
> > +				rxq->xsk_queue_idx, rxq->umem->umem,
> &rxq->rx,
> > +				&txq->tx, &cfg);
> > +	} else {
> > +		ret = xsk_socket__create_shared(&rxq->xsk, internals-
> >if_name,
> > +				rxq->xsk_queue_idx, rxq->umem->umem,
> &rxq->rx,
> > +				&txq->tx, &rxq->fq, &rxq->cq, &cfg);
> > +	}
> 
> Is the above dependency (ETH_AF_XDP_SHARED_UMEM) for the kernel
> 'af_xdp' code,
> or for 'libbpf.so'?
> 
> The 'xsk_socket__create_shared()' API is not available in the latest
> 'libbpf.so', I wonder if the kernel version check is to align with the correct
> 'libbpf.so' version.
> If not how the dependent version of the 'libbpf.so' managed for DPDK?

Good point.
For the RFC I'm assuming the user is using libbpf packaged with the kernel both with appropriate support.
In the next RFC/v1 I'll introduce a check for both the correct libbpf version and underlying kernel support, as both are required.

Thanks,
Ciara