[PATCH v1 2/2] perf auxtrace: Optimize barriers with load-acquire and store-release
From: Leo Yan <hidden>
Date: 2021-05-19 14:03:44
Also in:
lkml
Subsystem:
performance events subsystem, the rest · Maintainers:
Peter Zijlstra, Ingo Molnar, Arnaldo Carvalho de Melo, Namhyung Kim, Linus Torvalds
Load-acquire and store-release are one-way permeable barriers, which can be used to guarantee the memory ordering between accessing the buffer data and the buffer's head / tail. This patch optimizes the memory ordering with the load-acquire and store-release barriers. If the load-acquire is not supported by the architectures, it uses the existed READ_ONCE() + smp_rmb() pair rather than use the fallback definition of smp_load_acquire(). The reason is smp_rmb() is a minor improvement than smp_mb() which is called in the fallback macro smp_load_acquire(). In auxtrace_mmap__write_tail(), updating the tail pointer is removed; if the store-release barrier is not supported, it rollbacks to use smp_mb() + WRITE_ONCE() pair which is defined in the fallback macro smp_store_release() (see include/asm/barrier.h). Signed-off-by: Leo Yan <redacted> --- tools/perf/util/auxtrace.h | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-)
diff --git a/tools/perf/util/auxtrace.h b/tools/perf/util/auxtrace.h
index 8bed284ccc82..f18070f1993f 100644
--- a/tools/perf/util/auxtrace.h
+++ b/tools/perf/util/auxtrace.h@@ -449,16 +449,27 @@ struct auxtrace_cache; static inline u64 auxtrace_mmap__read_snapshot_head(struct auxtrace_mmap *mm) { struct perf_event_mmap_page *pc = mm->userpg; + +#if defined(__x86_64__) || defined(__aarch64__) || defined(__powerpc64__) || \ + defined(__ia64__) || defined(__sparc__) && defined(__arch64__) + return smp_load_acquire(&pc->aux_head); +#else u64 head = READ_ONCE(pc->aux_head); /* Ensure all reads are done after we read the head */ smp_rmb(); return head; +#endif } static inline u64 auxtrace_mmap__read_head(struct auxtrace_mmap *mm) { struct perf_event_mmap_page *pc = mm->userpg; + +#if defined(__x86_64__) || defined(__aarch64__) || defined(__powerpc64__) || \ + defined(__ia64__) || defined(__sparc__) && defined(__arch64__) + return smp_load_acquire(&pc->aux_head); +#else #if BITS_PER_LONG == 64 || !defined(HAVE_SYNC_COMPARE_AND_SWAP_SUPPORT) u64 head = READ_ONCE(pc->aux_head); #else
@@ -468,20 +479,20 @@ static inline u64 auxtrace_mmap__read_head(struct auxtrace_mmap *mm) /* Ensure all reads are done after we read the head */ smp_rmb(); return head; +#endif } static inline void auxtrace_mmap__write_tail(struct auxtrace_mmap *mm, u64 tail) { struct perf_event_mmap_page *pc = mm->userpg; -#if BITS_PER_LONG != 64 && defined(HAVE_SYNC_COMPARE_AND_SWAP_SUPPORT) + +#if BITS_PER_LONG == 64 || !defined(HAVE_SYNC_COMPARE_AND_SWAP_SUPPORT) + smp_store_release(&pc->aux_tail, tail); +#else u64 old_tail; -#endif /* Ensure all reads are done before we write the tail out */ smp_mb(); -#if BITS_PER_LONG == 64 || !defined(HAVE_SYNC_COMPARE_AND_SWAP_SUPPORT) - pc->aux_tail = tail; -#else do { old_tail = __sync_val_compare_and_swap(&pc->aux_tail, 0, 0); } while (!__sync_bool_compare_and_swap(&pc->aux_tail, old_tail, tail));
--
2.25.1