Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759513Ab1FWO0k (ORCPT ); Thu, 23 Jun 2011 10:26:40 -0400 Received: from merlin.infradead.org ([205.233.59.134]:39136 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758232Ab1FWO0j convert rfc822-to-8bit (ORCPT ); Thu, 23 Jun 2011 10:26:39 -0400 Subject: Re: [PATCH] events: Ensure that timers are updated without requiring read() call From: Peter Zijlstra To: Eric B Munson Cc: mingo@elte.hu, borislav.petkov@amd.com, bblum@andrew.cmu.edu, linux-kernel@vger.kernel.org, mhack@us.ibm.com In-Reply-To: <1308838537-6682-1-git-send-email-emunson@mgebm.net> References: <1308838537-6682-1-git-send-email-emunson@mgebm.net> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Thu, 23 Jun 2011 16:25:50 +0200 Message-ID: <1308839150.1022.130.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1435 Lines: 33 On Thu, 2011-06-23 at 10:15 -0400, Eric B Munson wrote: > The event tracing infrastructure exposes two timers which should be updated > each time the value of the counter is updated. Currently, these counters are > only updated when userspace calls read() on the fd associated with an event. > This means that counters which are read via the mmap'd page exclusively never > have their timers updated. This patch adds ensures that the timers are updated > each time the values in the mmap'd page are updated. > > Signed-off-by: Eric B Munson > --- > kernel/events/core.c | 1 + > 1 files changed, 1 insertions(+), 0 deletions(-) > > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 9efe710..3dd4ebe 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -3369,6 +3369,7 @@ void perf_event_update_userpage(struct perf_event *event) > struct perf_buffer *buffer; > > rcu_read_lock(); > + update_event_times(event); > buffer = rcu_dereference(event->buffer); > if (!buffer) > goto unlock; Not that easy, perf_event_update_userpage() can happen from NMI context, and update_event_times() needs to be done under ctx->lock. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/