From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 804D3C43381 for ; Wed, 27 Mar 2019 09:17:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 58A0E2075C for ; Wed, 27 Mar 2019 09:17:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732570AbfC0JRu (ORCPT ); Wed, 27 Mar 2019 05:17:50 -0400 Received: from mga14.intel.com ([192.55.52.115]:29121 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726257AbfC0JRs (ORCPT ); Wed, 27 Mar 2019 05:17:48 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by fmsmga103.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 27 Mar 2019 02:17:48 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.60,276,1549958400"; d="scan'208";a="331086745" Received: from um.fi.intel.com (HELO localhost) ([10.237.72.178]) by fmsmga006.fm.intel.com with ESMTP; 27 Mar 2019 02:17:44 -0700 From: Alexander Shishkin To: Ben Gainey , "mingo\@kernel.org" , "peterz\@infradead.org" , "acme\@redhat.com" , Will Deacon Cc: "linux-arm-kernel\@lists.infradead.org" , "linux-kernel\@vger.kernel.org" , alexander.shishkin@linux.intel.com Subject: Re: BUG in "perf: Suppress AUX/OVERWRITE records"? In-Reply-To: <3f04004a48a4b5bece9d277d5c51661f4eca7e97.camel@arm.com> References: <87k1gm86en.fsf@ashishki-desk.ger.corp.intel.com> <3f04004a48a4b5bece9d277d5c51661f4eca7e97.camel@arm.com> Date: Wed, 27 Mar 2019 11:17:43 +0200 Message-ID: <87wokk7k20.fsf@ashishki-desk.ger.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Ben Gainey writes: >> It was an unintentional side effect that it also >> happened to coincide with context switches in the overwrite mode. > > I'm not using overwrite mode, I'm opening the mmap with PROT_WRITE > (i.e. in truncate mode). Now I get it. Does the below fix the problem for you? >From bf52320cce0e74a2c0d987db7bd571f7687b4f4f Mon Sep 17 00:00:00 2001 From: Alexander Shishkin Date: Wed, 27 Mar 2019 11:05:53 +0200 Subject: [PATCH] perf: Fix AUX record suppression Commit 1627314fb54a33e ("perf: Suppress AUX/OVERWRITE records") has an unintended side-effect of also suppressing all AUX records with no flags and non-zero size, so all the regular records in the full trace mode. This breaks some use cases for people. Fix this by restoring "regular" AUX records to their former glory. Signed-off-by: Alexander Shishkin Fixes: 1627314fb54a33e ("perf: Suppress AUX/OVERWRITE records") Reported-by: Ben Gainey CC: stable@vger.kernel.org # v4.20+ --- kernel/events/ring_buffer.c | 33 +++++++++++++++------------------ 1 file changed, 15 insertions(+), 18 deletions(-) diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index 678ccec60d8f..626256dc26c1 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -455,24 +455,21 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size) rb->aux_head += size; } - if (size || handle->aux_flags) { - /* - * Only send RECORD_AUX if we have something useful to communicate - * - * Note: the OVERWRITE records by themselves are not considered - * useful, as they don't communicate any *new* information, - * aside from the short-lived offset, that becomes history at - * the next event sched-in and therefore isn't useful. - * The userspace that needs to copy out AUX data in overwrite - * mode should know to use user_page::aux_head for the actual - * offset. So, from now on we don't output AUX records that - * have *only* OVERWRITE flag set. - */ - - if (handle->aux_flags & ~(u64)PERF_AUX_FLAG_OVERWRITE) - perf_event_aux_event(handle->event, aux_head, size, - handle->aux_flags); - } + /* + * Only send RECORD_AUX if we have something useful to communicate + * + * Note: the OVERWRITE records by themselves are not considered + * useful, as they don't communicate any *new* information, + * aside from the short-lived offset, that becomes history at + * the next event sched-in and therefore isn't useful. + * The userspace that needs to copy out AUX data in overwrite + * mode should know to use user_page::aux_head for the actual + * offset. So, from now on we don't output AUX records that + * have *only* OVERWRITE flag set. + */ + if (size || (handle->aux_flags & ~(u64)PERF_AUX_FLAG_OVERWRITE)) + perf_event_aux_event(handle->event, aux_head, size, + handle->aux_flags); rb->user_page->aux_head = rb->aux_head; if (rb_need_aux_wakeup(rb)) -- 2.20.1