From mboxrd@z Thu Jan 1 00:00:00 1970 From: Uros Bizjak Subject: [PATCH v2 5/5] events: Illustrate the transition to local{,64}_try_cmpxchg Date: Wed, 5 Apr 2023 16:17:10 +0200 Message-ID: <20230405141710.3551-6-ubizjak@gmail.com> References: <20230405141710.3551-1-ubizjak@gmail.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; t=1680704276; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=tX2Wz3EA82OevW9OfamI7/Kvuo0JRd1kfWWZWf7tBPI=; b=dcJpf62STM2t7wBeMFWRHA65D4e8ki42FaDdkuuO3agKqVH6m85Cy4lQ8Jc6WqjxoF fnnlug9El9w16kuSLGTsPbq74oNaQ+P8JDxMAcNUZHQhE8u+5jySMEVYMmtE4egR+MrD Yo63AeJfrWzh2LWw4CUsO/Jz8F4pDt2KwqewSmosxEslt2xhDsBYXNkotYBZ0u2SUb3b bY44Ptodk1vZVbJl1WFw1p9lD7pDptPbaK3ykNtKWYarwScxbwyxAFGsy3vIZ++4+u08 7sJWtj5rpBofs9g4DRnm1uwhZ6aYf1PTSfC6VMfZ4+8IxgDtdbMLLd8hp6MXeYVptMAQ HEzw== In-Reply-To: <20230405141710.3551-1-ubizjak@gmail.com> List-ID: Content-Type: text/plain; charset="us-ascii" To: linux-alpha@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-arch@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Uros Bizjak This patch illustrates the transition to local{,64}_try_cmpxchg. It is not intended to be merged as-is. Signed-off-by: Uros Bizjak --- arch/x86/events/core.c | 9 ++++----- kernel/events/ring_buffer.c | 5 +++-- 2 files changed, 7 insertions(+), 7 deletions(-) diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index d096b04bf80e..d9310e9363f1 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -129,13 +129,12 @@ u64 x86_perf_event_update(struct perf_event *event) * exchange a new raw count - then add that new-prev delta * count to the generic event atomically: */ -again: prev_raw_count = local64_read(&hwc->prev_count); - rdpmcl(hwc->event_base_rdpmc, new_raw_count); - if (local64_cmpxchg(&hwc->prev_count, prev_raw_count, - new_raw_count) != prev_raw_count) - goto again; + do { + rdpmcl(hwc->event_base_rdpmc, new_raw_count); + } while (!local64_try_cmpxchg(&hwc->prev_count, &prev_raw_count, + new_raw_count)); /* * Now we have the new raw value and have updated the prev diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index 273a0fe7910a..111ab85ee97d 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -191,9 +191,10 @@ __perf_output_begin(struct perf_output_handle *handle, perf_output_get_handle(handle); + offset = local_read(&rb->head); do { tail = READ_ONCE(rb->user_page->data_tail); - offset = head = local_read(&rb->head); + head = offset; if (!rb->overwrite) { if (unlikely(!ring_buffer_has_space(head, tail, perf_data_size(rb), @@ -217,7 +218,7 @@ __perf_output_begin(struct perf_output_handle *handle, head += size; else head -= size; - } while (local_cmpxchg(&rb->head, offset, head) != offset); + } while (!local_try_cmpxchg(&rb->head, &offset, head)); if (backward) { offset = head; -- 2.39.2