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libbpf: remove dependency on barrier.h in xsk.h

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The use of smp_rmb() and smp_wmb() creates a Linux header dependency
on barrier.h that is unnecessary 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: 1cad078842 ("libbpf: add support for using AF_XDP sockets")
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Magnus Karlsson 2019-04-16 14:58:11 +02:00 committed by Alexei Starovoitov
parent a06d729646
commit b7e3a28019
2 changed files with 29 additions and 3 deletions
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25
tools/lib/bpf/libbpf_util.h
View File

@ -23,6 +23,31 @@ do { \
#define pr_info(fmt, ...) __pr(LIBBPF_INFO, fmt, ##__VA_ARGS__) #define pr_info(fmt, ...) __pr(LIBBPF_INFO, fmt, ##__VA_ARGS__)
#define pr_debug(fmt, ...) __pr(LIBBPF_DEBUG, fmt, ##__VA_ARGS__) #define pr_debug(fmt, ...) __pr(LIBBPF_DEBUG, fmt, ##__VA_ARGS__)
/* Use these barrier functions instead of smp_[rw]mb() when they are
* used in a libbpf header file. That way they can be built into the
* application that uses libbpf.
*/
#if defined(__i386__) || defined(__x86_64__)
# define libbpf_smp_rmb() asm volatile("" : : : "memory")
# define libbpf_smp_wmb() asm volatile("" : : : "memory")
# define libbpf_smp_mb() \
asm volatile("lock; addl $0,-4(%%rsp)" : : : "memory", "cc")
#elif defined(__aarch64__)
# define libbpf_smp_rmb() asm volatile("dmb ishld" : : : "memory")
# define libbpf_smp_wmb() asm volatile("dmb ishst" : : : "memory")
# define libbpf_smp_mb() asm volatile("dmb ish" : : : "memory")
#elif defined(__arm__)
/* These are only valid for armv7 and above */
# define libbpf_smp_rmb() asm volatile("dmb ish" : : : "memory")
# define libbpf_smp_wmb() asm volatile("dmb ishst" : : : "memory")
# define libbpf_smp_mb() asm volatile("dmb ish" : : : "memory")
#else
# warning Architecture missing native barrier functions in libbpf_util.h.
# define libbpf_smp_rmb() __sync_synchronize()
# define libbpf_smp_wmb() __sync_synchronize()
# define libbpf_smp_mb() __sync_synchronize()
#endif
#ifdef __cplusplus #ifdef __cplusplus
} /* extern "C" */ } /* extern "C" */
#endif #endif

7
tools/lib/bpf/xsk.h
View File

@ -16,6 +16,7 @@
#include <linux/if_xdp.h> #include <linux/if_xdp.h>
#include "libbpf.h" #include "libbpf.h"
#include "libbpf_util.h"
#ifdef __cplusplus #ifdef __cplusplus
extern "C" { extern "C" {
@ -123,7 +124,7 @@ 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 indicating /* Make sure everything has been written to the ring before indicating
* this to the kernel by writing the producer pointer. * this to the kernel by writing the producer pointer.
*/ */
smp_wmb(); libbpf_smp_wmb();
*prod->producer += nb; *prod->producer += nb;
} }
@ -137,7 +138,7 @@ static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons,
/* Make sure we do not speculatively read the data before /* Make sure we do not speculatively read the data before
* we have received the packet buffers from the ring. * we have received the packet buffers from the ring.
*/ */
smp_rmb(); libbpf_smp_rmb();
*idx = cons->cached_cons; *idx = cons->cached_cons;
cons->cached_cons += entries; cons->cached_cons += entries;
@ -151,7 +152,7 @@ static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, size_t nb)
/* Make sure data has been read before indicating we are done /* Make sure data has been read before indicating we are done
* with the entries by updating the consumer pointer. * with the entries by updating the consumer pointer.
*/ */
smp_mb(); libbpf_smp_mb();
*cons->consumer += nb; *cons->consumer += nb;
} }