On Wed, Sep 4, 2019 at 7:32 AM Yauheni Kaliuta
<yauheni.kaliuta@xxxxxxxxxx> wrote:
>
> Hi, Magnus!
>
> >>>>> On Tue, 9 Apr 2019 08:44:13 +0200, Magnus Karlsson wrote:
>
> > The use of smp_rmb() and smp_wmb() creates a Linux header dependency
> > on barrier.h that is uneccessary in most parts. This patch implements
> > the two small defines that are needed from barrier.h. As a bonus, the
> > new implementations are faster than the default ones as they default
> > to sfence and lfence for x86, while we only need a compiler barrier in
> > our case. Just as it is when the same ring access code is compiled in
> > the kernel.
>
> > Fixes: 1cad07884239 ("libbpf: add support for using AF_XDP sockets")
> > Signed-off-by: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>
> > ---
> > tools/lib/bpf/xsk.h | 19 +++++++++++++++++--
> > 1 file changed, 17 insertions(+), 2 deletions(-)
>
> > diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
> > index 3638147..317b44f 100644
> > --- a/tools/lib/bpf/xsk.h
> > +++ b/tools/lib/bpf/xsk.h
> > @@ -39,6 +39,21 @@ DEFINE_XSK_RING(xsk_ring_cons);
> > struct xsk_umem;
> > struct xsk_socket;
>
> > +#if !defined bpf_smp_rmb && !defined bpf_smp_wmb
> > +# if defined(__i386__) || defined(__x86_64__)
> > +# define bpf_smp_rmb() asm volatile("" : : : "memory")
> > +# define bpf_smp_wmb() asm volatile("" : : : "memory")
> > +# elif defined(__aarch64__)
> > +# define bpf_smp_rmb() asm volatile("dmb ishld" : : : "memory")
> > +# define bpf_smp_wmb() asm volatile("dmb ishst" : : : "memory")
> > +# elif defined(__arm__)
> > +# define bpf_smp_rmb() asm volatile("dmb ish" : : : "memory")
> > +# define bpf_smp_wmb() asm volatile("dmb ishst" : : : "memory")
> > +# else
> > +# error Architecture not supported by the XDP socket code in libbpf.
> > +# endif
> > +#endif
> > +
>
> What about other architectures then?
AF_XDP has not been tested on anything else, as far as I know. But
contributions that extend it to more archs are very welcome.
/Magnus
>
> > static inline __u64 *xsk_ring_prod__fill_addr(struct xsk_ring_prod *fill,
> > __u32 idx)
> > {
> > @@ -119,7 +134,7 @@ static inline void xsk_ring_prod__submit(struct xsk_ring_prod *prod, size_t nb)
> > /* Make sure everything has been written to the ring before signalling
> > * this to the kernel.
> > */
> > - smp_wmb();
> > + bpf_smp_wmb();
>
> > *prod->producer += nb;
> > }
> > @@ -133,7 +148,7 @@ static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons,
> > /* Make sure we do not speculatively read the data before
> > * we have received the packet buffers from the ring.
> > */
> > - smp_rmb();
> > + bpf_smp_rmb();
>
> > *idx = cons->cached_cons;
> cons-> cached_cons += entries;
> > --
> > 2.7.4
>
>
> --
> WBR,
> Yauheni Kaliuta
