From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754577AbYIWPFu (ORCPT ); Tue, 23 Sep 2008 11:05:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753971AbYIWPFk (ORCPT ); Tue, 23 Sep 2008 11:05:40 -0400 Received: from mx1.redhat.com ([66.187.233.31]:57147 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753908AbYIWPFj (ORCPT ); Tue, 23 Sep 2008 11:05:39 -0400 Date: Tue, 23 Sep 2008 11:02:09 -0400 From: "Frank Ch. Eigler" To: KOSAKI Motohiro Cc: Masami Hiramatsu , Martin Bligh , Linux Kernel Mailing List , Linus Torvalds , Thomas Gleixner , Mathieu Desnoyers , Steven Rostedt , od@novell.com, systemtap-ml Subject: Re: Unified tracing buffer Message-ID: <20080923150209.GF29900@redhat.com> References: <33307c790809221313s3532d851g7239c212bc72fe71@mail.gmail.com> <48D81B5F.2030702@redhat.com> <20080923232239.DC1E.KOSAKI.MOTOHIRO@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080923232239.DC1E.KOSAKI.MOTOHIRO@jp.fujitsu.com> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi - On Tue, Sep 23, 2008 at 11:36:26PM +0900, KOSAKI Motohiro wrote: > > By the way, systemtap uses two modes; > > > > - single-channel mode > > In this mode, all cpus share one buffer channel to write and read. > > each writer locks spinlock and write a probe-local data to buffer. > > - per-cpu buffer mode [...] > > I can't imazine a merit of the single-channel mode. > Could you please explain it? It could be a way of saving some memory and merging hassle for low-throughput data. (Remember that systemtap enables in-situ analysis of events so that often only brief final results need be sent along need be sent out.) If timestampwise cross-cpu merging can be done on demand by the hypothetical future buffer widget, then little reason remains not to use it. - FChE