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 | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)
diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
index 3638147..69136d9 100644
--- a/tools/lib/bpf/xsk.h
+++ b/tools/lib/bpf/xsk.h
@@ -39,6 +39,22 @@ 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__)
+/* These are only valid for armv7 and above */
+# 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
+
static inline __u64 *xsk_ring_prod__fill_addr(struct xsk_ring_prod *fill,
__u32 idx)
{
@@ -119,7 +135,7 @@ 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 +149,7 @@ 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
