From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Mundt Subject: Re: [patch 0/3] [Announcement] Performance Counters for Linux Date: Wed, 10 Dec 2008 12:48:24 +0900 Message-ID: <20081210034824.GA27217@linux-sh.org> References: <20081205.002701.172921476.davem@davemloft.net> <20081205084233.GE2030@elte.hu> <87ej0mx0c0.fsf@basil.nowhere.org> <20081205.120814.51226316.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mta23.gyao.ne.jp ([125.63.38.249]:11712 "EHLO mx.gate01.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754634AbYLJDun (ORCPT ); Tue, 9 Dec 2008 22:50:43 -0500 Content-Disposition: inline In-Reply-To: <20081205.120814.51226316.davem@davemloft.net> Sender: linux-arch-owner@vger.kernel.org List-ID: To: David Miller Cc: andi@firstfloor.org, mingo@elte.hu, a.p.zijlstra@chello.nl, paulus@samba.org, tglx@linutronix.de, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, akpm@linux-foundation.org, eranian@googlemail.com, dada1@cosmosbay.com, robert.richter@amd.com, arjan@infradead.org, hpa@zytor.com, rostedt@goodmis.org On Fri, Dec 05, 2008 at 12:08:14PM -0800, David Miller wrote: > From: Andi Kleen > Date: Fri, 05 Dec 2008 13:39:43 +0100 > > > Given these are more obscure features, but not being able to fit > > them easily into your model from the start isn't a very promising sign > > for the long term extensibility of the design. > > Another thing I'm interested in is if this new stuff will work with > performance counters that lack an overflow interrupt. > > We have several chips that are like this, and perfmon supported that > on the kernel side, and also provided overflow emulation for such > hardware in userspace (where such complexity belongs). There doesn't seem to have been any reply to this point unfortunately, and it is something I am also wondering about. The sh perf counters were not designed with overflowing in mind, they are split in to a pair of 48-bit or 64-bit counters that simply keep running. Any write simply clears the value and the counter starts over. They are simply counters only, and generate no events whatsoever. Oprofile has been a pretty bad fit for them, and while I'm slightly more optimistic about perfmon, I'm rather less enthusiastic about yet another peformance counter implementation that I am unable to make any use of.