From: Leo Yan <leo.yan@linaro.org>
To: Arnaldo Carvalho de Melo <acme@kernel.org>,
Adrian Hunter <adrian.hunter@intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Namhyung Kim <namhyung@kernel.org>,
Andi Kleen <ak@linux.intel.com>,
linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: Leo Yan <leo.yan@linaro.org>
Subject: [PATCH v1 2/2] perf auxtrace: Optimize barriers with load-acquire and store-release
Date: Wed, 19 May 2021 22:03:19 +0800 [thread overview]
Message-ID: <20210519140319.1673043-2-leo.yan@linaro.org> (raw)
In-Reply-To: <20210519140319.1673043-1-leo.yan@linaro.org>
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 <leo.yan@linaro.org>
---
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
next prev parent reply other threads:[~2021-05-19 14:03 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-19 14:03 [PATCH v1 1/2] perf auxtrace: Change to use SMP memory barriers Leo Yan
2021-05-19 14:03 ` Leo Yan [this message]
2021-05-31 15:10 ` [PATCH v1 2/2] perf auxtrace: Optimize barriers with load-acquire and store-release Leo Yan
2021-05-31 15:55 ` Peter Zijlstra
2021-05-31 19:03 ` Adrian Hunter
2021-06-01 6:33 ` Leo Yan
2021-06-01 6:58 ` Peter Zijlstra
2021-06-01 9:07 ` Adrian Hunter
2021-06-01 9:17 ` Peter Zijlstra
2021-06-01 9:45 ` Adrian Hunter
2021-06-01 9:48 ` Peter Zijlstra
2021-06-01 14:56 ` Leo Yan
2021-06-01 6:48 ` Peter Zijlstra
2021-05-27 7:54 ` [PATCH v1 1/2] perf auxtrace: Change to use SMP memory barriers Adrian Hunter
2021-05-27 8:11 ` Peter Zijlstra
2021-05-27 8:25 ` Adrian Hunter
2021-05-27 9:24 ` Adrian Hunter
2021-05-27 9:57 ` Peter Zijlstra
2021-05-31 14:53 ` Leo Yan
2021-05-31 15:48 ` Peter Zijlstra
2021-06-01 3:21 ` Leo Yan
2021-05-27 9:45 ` Peter Zijlstra
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