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selftests/xsk: replace asm acquire/release implementations 

Replace our own homegrown assembly store/release and load/acquire
implementations with the HW agnositic atomic APIs C11 offers. This to
make the code more portable, easier to read, and reduce the
maintenance burden.

The original code used load-acquire and store-release barriers
hand-coded in assembly. Since C11, these kind of operations are
offered as built-ins in gcc and llvm. The load-acquire operation
prevents hoisting of non-atomic memory operations to before this
operation and it corresponds to the __ATOMIC_ACQUIRE operation in the
built-in atomics. The store-release operation prevents hoisting of
non-atomic memory operations to after this operation and it
corresponds to the __ATOMIC_RELEASE operation in the built-in atomics.

Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Acked-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Link: https://lore.kernel.org/r/20230111093526.11682-8-magnus.karlsson@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Magnus Karlsson 2023-01-11 10:35:18 +01:00 committed by Alexei Starovoitov
parent 703bfd3710
commit efe620e5ba
1 changed files with 4 additions and 76 deletions
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80
tools/testing/selftests/bpf/xsk.h
View File

@ -23,77 +23,6 @@
extern "C" {
#endif
/* This whole API has been deprecated and moved to libxdp that can be found at
* https://github.com/xdp-project/xdp-tools. The APIs are exactly the same so
* it should just be linking with libxdp instead of libbpf for this set of
* functionality. If not, please submit a bug report on the aforementioned page.
*/
/* Load-Acquire Store-Release barriers used by the XDP socket
* library. The following macros should *NOT* be considered part of
* the xsk.h API, and is subject to change anytime.
*
* LIBRARY INTERNAL
*/
#define __XSK_READ_ONCE(x) (*(volatile typeof(x) *)&x)
#define __XSK_WRITE_ONCE(x, v) (*(volatile typeof(x) *)&x) = (v)
#if defined(__i386__) || defined(__x86_64__)
# define libbpf_smp_store_release(p, v) \
do { \
asm volatile("" : : : "memory"); \
__XSK_WRITE_ONCE(*p, v); \
} while (0)
# define libbpf_smp_load_acquire(p) \
({ \
typeof(*p) ___p1 = __XSK_READ_ONCE(*p); \
asm volatile("" : : : "memory"); \
___p1; \
})
#elif defined(__aarch64__)
# define libbpf_smp_store_release(p, v) \
asm volatile ("stlr %w1, %0" : "=Q" (*p) : "r" (v) : "memory")
# define libbpf_smp_load_acquire(p) \
({ \
typeof(*p) ___p1; \
asm volatile ("ldar %w0, %1" \
: "=r" (___p1) : "Q" (*p) : "memory"); \
___p1; \
})
#elif defined(__riscv)
# define libbpf_smp_store_release(p, v) \
do { \
asm volatile ("fence rw,w" : : : "memory"); \
__XSK_WRITE_ONCE(*p, v); \
} while (0)
# define libbpf_smp_load_acquire(p) \
({ \
typeof(*p) ___p1 = __XSK_READ_ONCE(*p); \
asm volatile ("fence r,rw" : : : "memory"); \
___p1; \
})
#endif
#ifndef libbpf_smp_store_release
#define libbpf_smp_store_release(p, v) \
do { \
__sync_synchronize(); \
__XSK_WRITE_ONCE(*p, v); \
} while (0)
#endif
#ifndef libbpf_smp_load_acquire
#define libbpf_smp_load_acquire(p) \
({ \
typeof(*p) ___p1 = __XSK_READ_ONCE(*p); \
__sync_synchronize(); \
___p1; \
})
#endif
/* LIBRARY INTERNAL -- END */
/* Do not access these members directly. Use the functions below. */
#define DEFINE_XSK_RING(name) \
struct name { \
@ -168,7 +97,7 @@ static inline __u32 xsk_prod_nb_free(struct xsk_ring_prod *r, __u32 nb)
* this function. Without this optimization it whould have been
* free_entries = r->cached_prod - r->cached_cons + r->size.
*/
r->cached_cons = libbpf_smp_load_acquire(r->consumer);
r->cached_cons = __atomic_load_n(r->consumer, __ATOMIC_ACQUIRE);
r->cached_cons += r->size;
return r->cached_cons - r->cached_prod;
@ -179,7 +108,7 @@ static inline __u32 xsk_cons_nb_avail(struct xsk_ring_cons *r, __u32 nb)
__u32 entries = r->cached_prod - r->cached_cons;
if (entries == 0) {
r->cached_prod = libbpf_smp_load_acquire(r->producer);
r->cached_prod = __atomic_load_n(r->producer, __ATOMIC_ACQUIRE);
entries = r->cached_prod - r->cached_cons;
}
@ -202,7 +131,7 @@ static inline void xsk_ring_prod__submit(struct xsk_ring_prod *prod, __u32 nb)
/* Make sure everything has been written to the ring before indicating
* this to the kernel by writing the producer pointer.
*/
libbpf_smp_store_release(prod->producer, *prod->producer + nb);
__atomic_store_n(prod->producer, *prod->producer + nb, __ATOMIC_RELEASE);
}
static inline __u32 xsk_ring_cons__peek(struct xsk_ring_cons *cons, __u32 nb, __u32 *idx)
@ -227,8 +156,7 @@ static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, __u32 nb)
/* Make sure data has been read before indicating we are done
* with the entries by updating the consumer pointer.
*/
libbpf_smp_store_release(cons->consumer, *cons->consumer + nb);
__atomic_store_n(cons->consumer, *cons->consumer + nb, __ATOMIC_RELEASE);
}
static inline void *xsk_umem__get_data(void *umem_area, __u64 addr)