From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753390AbYIZRJa (ORCPT ); Fri, 26 Sep 2008 13:09:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752018AbYIZRJW (ORCPT ); Fri, 26 Sep 2008 13:09:22 -0400 Received: from mx1.redhat.com ([66.187.233.31]:46030 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751999AbYIZRJV (ORCPT ); Fri, 26 Sep 2008 13:09:21 -0400 Message-ID: <48DD1475.1090109@redhat.com> Date: Fri, 26 Sep 2008 12:57:25 -0400 From: Masami Hiramatsu User-Agent: Thunderbird 2.0.0.16 (X11/20080723) MIME-Version: 1.0 To: Peter Zijlstra CC: Steven Rostedt , Mathieu Desnoyers , LKML , Ingo Molnar , Thomas Gleixner , Andrew Morton , prasad@linux.vnet.ibm.com, Linus Torvalds , "Frank Ch. Eigler" , David Wilder , hch@lst.de, Martin Bligh , Christoph Hellwig , Steven Rostedt Subject: Re: [RFC PATCH v4] Unified trace buffer References: <20080925185154.230259579@goodmis.org> <20080925185236.244343232@goodmis.org> <48DC406D.1050508@redhat.com> <20080926032045.GA28771@Krystal> <1222413507.16700.235.camel@lappy.programming.kicks-ass.net> <1222426855.16700.264.camel@lappy.programming.kicks-ass.net> In-Reply-To: <1222426855.16700.264.camel@lappy.programming.kicks-ass.net> X-Enigmail-Version: 0.95.7 Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Peter Zijlstra wrote: > On Fri, 2008-09-26 at 06:45 -0400, Steven Rostedt wrote: >> On Fri, 26 Sep 2008, Peter Zijlstra wrote: >>> On Thu, 2008-09-25 at 23:20 -0400, Mathieu Desnoyers wrote: >>>> You could also fallback on a 2-level page array when buffer size is > >>>> 64MB. The cost is mainly a supplementary pointer dereference, but one >>>> more should not make sure a big difference overall. >>> I'm still not sure why we don't just link the pages using the page >>> frames, we don't need the random access, do we? >> Yeah we can go back to that (as ftrace does). >> >> 1) It can be very error prone. I will need to encapsulate the logic more. > > Sure. > >> 2) I'm still not sure if crash can handle it. > > It ought to, and if it can't it should be fixed. Having easy access to > the pageframes is vital to debugging VM issues. So I'd not bother about > this issue too much. > >> I was going to reply to Masami with this answer, but it makes things more >> complex. For v1 (non RFC v1) I wanted to start simple. v2 can have this >> enhancement. > > Right - I just object to having anything vmalloc. I just requested that the expansion of buffer size limitation too. :) I don't stick with vmalloc. If that (page frame chain?) can achieve better performance, I agree that trace buffer uses it. Thank you, -- Masami Hiramatsu Software Engineer Hitachi Computer Products (America) Inc. Software Solutions Division e-mail: mhiramat@redhat.com