From mboxrd@z Thu Jan 1 00:00:00 1970 From: "David S. Ahern" Subject: Re: [PATCH 1/2] perf tools: Add reference timestamp to perf header Date: Mon, 13 Dec 2010 11:20:55 -0700 Message-ID: <4D066407.3040707@cisco.com> References: <1291773285-16254-1-git-send-email-daahern@cisco.com> <1291773285-16254-2-git-send-email-daahern@cisco.com> <20101212201613.GA1784@nowhere> <4D06301C.2090309@cisco.com> <20101213155451.GA1691@nowhere> <20101213164854.GL5407@ghostprotocols.net> <20101213170923.GB1691@nowhere> <1292260289.6803.297.camel@twins> <20101213171537.GC1691@nowhere> <1292260699.6803.305.camel@twins> <20101213172216.GB7417@ghostprotocols.net> <1292261716.6803.332.camel@twins> <1292262433.6803.351.camel@twins> <4D065CB2.7050104@cisco.com> <1292263024.6803.370.camel@twins> <4D065F69.7080707@cisco.com> <1292263573.6803.381.camel@twins> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: Received: from sj-iport-1.cisco.com ([171.71.176.70]:49112 "EHLO sj-iport-1.cisco.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757654Ab0LMSU7 (ORCPT ); Mon, 13 Dec 2010 13:20:59 -0500 In-Reply-To: <1292263573.6803.381.camel@twins> Sender: linux-perf-users-owner@vger.kernel.org List-ID: To: Peter Zijlstra Cc: Arnaldo Carvalho de Melo , Frederic Weisbecker , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org On 12/13/10 11:06, Peter Zijlstra wrote: > On Mon, 2010-12-13 at 11:01 -0700, David S. Ahern wrote: >>> Another problem with this approach is things like flight-recorder mode >>> where you constantly over-write your old data, you'd have to build some >>> trigger to always output a new record before you over-write the old one, >>> so there's always one consistent record around. Drift is an even more >>> serious problem here since flight-record more could be running for days >>> before (if ever) you dump it. >> >> Ok. I was not aware flight-recorder mode was an option today. > > You get it when you mmap the fd RO -- the only thing is you don't get a > consistent tail pointer so you have to fudge a bit. Awesome. Flight recorder mode is on our wish list. I'll try it out when I get some time. David > > But even if we didn't have it, we'd need a solution that would work once > we did grow it ;-)