From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751680AbdGaKcU (ORCPT ); Mon, 31 Jul 2017 06:32:20 -0400 Received: from mga11.intel.com ([192.55.52.93]:60690 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750920AbdGaKcT (ORCPT ); Mon, 31 Jul 2017 06:32:19 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.40,441,1496127600"; d="scan'208";a="999089132" From: Alexander Shishkin To: Will Deacon , linux-kernel@vger.kernel.org Cc: mark.rutland@arm.com, linux-arm-kernel@lists.infradead.org, Will Deacon , Peter Zijlstra Subject: Re: [PATCH 1/2] perf/aux: Make aux_{head,wakeup} ring_buffer members long In-Reply-To: <1501260863-14687-1-git-send-email-will.deacon@arm.com> References: <1501260863-14687-1-git-send-email-will.deacon@arm.com> User-Agent: Notmuch/0.23.7 (http://notmuchmail.org) Emacs/24.5.1 (x86_64-pc-linux-gnu) Date: Mon, 31 Jul 2017 13:28:01 +0300 Message-ID: <87ini8uci6.fsf@ashishki-desk.ger.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Will Deacon writes: > The aux_head and aux_wakeup members of struct ring_buffer are defined > using the local_t type, despite the fact that they are only accessed via > the perf_aux_output_* functions, which cannot race with each other for a > given ring buffer. > > This patch changes the type of the members to long, so we can avoid > using the local_* API where it isn't needed. Thanks for digging this up! Some minor nits below. > @@ -434,12 +434,12 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size) > handle->aux_flags |= PERF_AUX_FLAG_OVERWRITE; > > aux_head = handle->head; > - local_set(&rb->aux_head, aux_head); > + rb->aux_head = aux_head; > } else { > handle->aux_flags &= ~PERF_AUX_FLAG_OVERWRITE; > > - aux_head = local_read(&rb->aux_head); > - local_add(size, &rb->aux_head); > + aux_head = rb->aux_head; > + rb->aux_head += size; > } > > if (size || handle->aux_flags) { > @@ -451,11 +451,11 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size) > handle->aux_flags); > } > > - aux_head = rb->user_page->aux_head = local_read(&rb->aux_head); > + aux_head = rb->user_page->aux_head = rb->aux_head; > > - if (aux_head - local_read(&rb->aux_wakeup) >= rb->aux_watermark) { > + if (aux_head - rb->aux_wakeup >= rb->aux_watermark) { Can't we just do away with aux_head here: rb->user_page->aux_head = rb->aux_head; if (rb->aux_head - rb->aux_wakeup >= rb->aux_watermark) { ... ? > @@ -485,14 +485,13 @@ int perf_aux_output_skip(struct perf_output_handle *handle, unsigned long size) > if (size > handle->size) > return -ENOSPC; > > - local_add(size, &rb->aux_head); > + rb->aux_head += size; > > - aux_head = rb->user_page->aux_head = local_read(&rb->aux_head); > - if (aux_head - local_read(&rb->aux_wakeup) >= rb->aux_watermark) { > + aux_head = rb->user_page->aux_head = rb->aux_head; > + if (aux_head - rb->aux_wakeup >= rb->aux_watermark) { > perf_output_wakeup(handle); > - local_add(rb->aux_watermark, &rb->aux_wakeup); > - handle->wakeup = local_read(&rb->aux_wakeup) + > - rb->aux_watermark; > + rb->aux_wakeup += rb->aux_watermark; > + handle->wakeup = rb->aux_wakeup + rb->aux_watermark; > } > > handle->head = aux_head; And here I think we don't need aux_head at all. Thanks, -- Alex