RE: [PATCH] net/af_xdp: fix umem map size for zero copy

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

> >
> > > Subject: [PATCH] net/af_xdp: fix umem map size for zero copy
> > >
> > > The current calculation assumes that the mbufs are contiguous.
> > > However, this assumption is incorrect when the memory spans across a
> huge
> > page.
> > > Correct to directly read the size from the mempool memory chunks.
> > >
> > > Signed-off-by: Frank Du <frank.du@intel.com>
> > > ---
> > >  drivers/net/af_xdp/rte_eth_af_xdp.c | 10 +++++-----
> > >  1 file changed, 5 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/net/af_xdp/rte_eth_af_xdp.c
> > > b/drivers/net/af_xdp/rte_eth_af_xdp.c
> > > index 268a130c49..cb95d17d13 100644
> > > --- a/drivers/net/af_xdp/rte_eth_af_xdp.c
> > > +++ b/drivers/net/af_xdp/rte_eth_af_xdp.c
> > > @@ -1039,7 +1039,7 @@ eth_link_update(struct rte_eth_dev *dev
> > > __rte_unused,  }
> > >
> > >  #if defined(XDP_UMEM_UNALIGNED_CHUNK_FLAG)
> > > -static inline uintptr_t get_base_addr(struct rte_mempool *mp,
> > > uint64_t
> > > *align)
> > > +static inline uintptr_t get_memhdr_info(struct rte_mempool *mp,
> > > +uint64_t
> > > *align, size_t *len)
> > >  {
> > >  	struct rte_mempool_memhdr *memhdr;
> > >  	uintptr_t memhdr_addr, aligned_addr; @@ -1048,6 +1048,7 @@
> static
> > > inline uintptr_t get_base_addr(struct rte_mempool *mp, uint64_t
> > > *align)
> > >  	memhdr_addr = (uintptr_t)memhdr->addr;
> > >  	aligned_addr = memhdr_addr & ~(getpagesize() - 1);
> > >  	*align = memhdr_addr - aligned_addr;
> > > +	*len = memhdr->len;
> > >
> > >  	return aligned_addr;
> > >  }
> > > @@ -1125,6 +1126,7 @@ xsk_umem_info *xdp_umem_configure(struct
> > > pmd_internals *internals,
> > >  	void *base_addr = NULL;
> > >  	struct rte_mempool *mb_pool = rxq->mb_pool;
> > >  	uint64_t umem_size, align = 0;
> > > +	size_t len = 0;
> > >
> > >  	if (internals->shared_umem) {
> > >  		if (get_shared_umem(rxq, internals->if_name, &umem) < 0)
> @@
> > > -1156,10 +1158,8 @@ xsk_umem_info *xdp_umem_configure(struct
> > > pmd_internals *internals,
> > >  		}
> > >
> > >  		umem->mb_pool = mb_pool;
> > > -		base_addr = (void *)get_base_addr(mb_pool, &align);
> > > -		umem_size = (uint64_t)mb_pool->populated_size *
> > > -				(uint64_t)usr_config.frame_size +
> > > -				align;
> > > +		base_addr = (void *)get_memhdr_info(mb_pool, &align,
> > > &len);
> > > +		umem_size = (uint64_t)len + align;
> >
> > len is set to the length of the first memhdr of the mempool. There may be
> many
> > other memhdrs in the mempool. So I don't think this is the correct value to
> use for
> > calculating the entire umem size.
> 
> Current each xdp rx ring is bonded to one single umem region, it can't reuse
> the memory
> if there are multiple memhdrs in the mempool. How about adding a check on
> the number
> of the memory chunks to only allow one single memhdr mempool can be used
> here?

The UMEM needs to be a region of virtual contiguous memory. I think this can still be the case, even if the mempool has multiple memhdrs.
If we detect >1 memhdrs perhaps we need to verify that the RTE_MEMPOOL_F_NO_IOVA_CONTIG flag is not set which I think would mean that the mempool may not be virtually contiguous.

> 
> >
> > >
> > >  		ret = xsk_umem__create(&umem->umem, base_addr,
> > umem_size,
> > >  				&rxq->fq, &rxq->cq, &usr_config);
> > > --
> > > 2.34.1