Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753742AbYKZBJo (ORCPT ); Tue, 25 Nov 2008 20:09:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752008AbYKZBJd (ORCPT ); Tue, 25 Nov 2008 20:09:33 -0500 Received: from fgwmail7.fujitsu.co.jp ([192.51.44.37]:51485 "EHLO fgwmail7.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751255AbYKZBJc (ORCPT ); Tue, 25 Nov 2008 20:09:32 -0500 From: KOSAKI Motohiro To: Mathieu Desnoyers Subject: Re: [PATCH] Poll : introduce poll_wait_exclusive() new function Cc: kosaki.motohiro@jp.fujitsu.com, Ingo Molnar , ltt-dev@lists.casi.polymtl.ca, Linux Kernel Mailing List , William Lee Irwin III , Davide Libenzi In-Reply-To: References: <20081125194700.26EB.KOSAKI.MOTOHIRO@jp.fujitsu.com> Message-Id: <20081126100749.3CAC.KOSAKI.MOTOHIRO@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.42 [ja] Date: Wed, 26 Nov 2008 10:09:29 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1297 Lines: 26 > > Mathieu Desnoyers explained it cause following problem to LTTng. > > > > In LTTng, all lttd readers are polling all the available debugfs files > > for data. This is principally because the number of reader threads is > > user-defined and there are typical workloads where a single CPU is > > producing most of the tracing data and all other CPUs are idle, > > available to consume data. It therefore makes sense not to tie those > > threads to specific buffers. However, when the number of threads grows, > > we face a "thundering herd" problem where many threads can be woken up > > and put back to sleep, leaving only a single thread doing useful work. > > Why do you need to have so many threads banging a single device/file? > Have one (or any other very little number) puller thread(s), that > activates with chucks of pulled data the other processing threads. That > way there's no need for a new wakeup abstraction. Mathieu, I don't hope I unstrictly explain to LTTng. Could you please explain LTTng design? -- 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/