Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752347Ab3DOOKY (ORCPT ); Mon, 15 Apr 2013 10:10:24 -0400 Received: from mail-la0-f42.google.com ([209.85.215.42]:52619 "EHLO mail-la0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751253Ab3DOOKX (ORCPT ); Mon, 15 Apr 2013 10:10:23 -0400 MIME-Version: 1.0 In-Reply-To: References: Date: Mon, 15 Apr 2013 16:10:21 +0200 Message-ID: Subject: Re: Trouble with full nohz and lttng From: Frederic Weisbecker To: Mats Liljegren Cc: linux-kernel@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1196 Lines: 24 2013/4/15 Mats Liljegren : > When I use lttng, I keep getting ticks. Without lttng, no ticks. It's the > same application I run, the same way. The only difference is whether lttng > logging has been started or not. > > The trace says "sched" as reason for not disabled ticks. Using "top" I can't > see any extra process/thread being created while my application runs, my > application gets 99-101% of the CPU. There are a couple of kworker threads > (3), a migration thread and a ksoftirq thread on the same CPU as my > application, though "top" gives no indication that they do any execution. > > Is this a known limitation of lttng, or is there something else going on > here? I have no idea. But the "sched" reason means there is more than one task in the runqueue at some point. It can be a kthread indeed. Or a user task that gets migrated / woken up in the CPU. You'll need to check the sched:sched_switch tracepoint. -- 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/