From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754481AbYIZCHa (ORCPT ); Thu, 25 Sep 2008 22:07:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752353AbYIZCHW (ORCPT ); Thu, 25 Sep 2008 22:07:22 -0400 Received: from gw.goop.org ([64.81.55.164]:34208 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751506AbYIZCHV (ORCPT ); Thu, 25 Sep 2008 22:07:21 -0400 Message-ID: <48DC43D7.5010008@goop.org> Date: Thu, 25 Sep 2008 19:07:19 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.16 (X11/20080723) MIME-Version: 1.0 To: Steven Rostedt CC: Linus Torvalds , Ingo Molnar , Martin Bligh , Peter Zijlstra , Martin Bligh , linux-kernel@vger.kernel.org, Thomas Gleixner , Andrew Morton , prasad@linux.vnet.ibm.com, Mathieu Desnoyers , "Frank Ch. Eigler" , David Wilder , hch@lst.de, Tom Zanussi , Steven Rostedt Subject: Re: [RFC PATCH 1/3] Unified trace buffer References: <33307c790809241403w236f2242y18ba44982d962287@mail.gmail.com> <1222339303.16700.197.camel@lappy.programming.kicks-ass.net> <8f3aa8d60809250733q70561e6agfa3b00da83773e9f@mail.gmail.com> <1222354409.16700.215.camel@lappy.programming.kicks-ass.net> <33307c790809250825u567d3680w682899c111e10ed6@mail.gmail.com> <20080925153635.GA12840@elte.hu> <48DBFC7D.4050208@goop.org> <48DC1338.6050107@goop.org> <48DC3A89.9020407@goop.org> In-Reply-To: X-Enigmail-Version: 0.95.7 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Steven Rostedt wrote: > OK, let me rephrase my question. > > How and where do we record this? Do we keep this information in some > global variable that we must compare to every time we add a new item in > the trace? > > Do we have the buffer register a call back to record this information? > Something like (total pseudocode): struct tsc_time_parameters { int version; /* even - values OK; odd - values being updated */ u64 tsc; u32 tsc_freq; u64 gtod; }; DEFINE_PERCPU(struct tsc_time_parameters, tsc_params); /* To be called after a tsc frequency change, before any new trace records are being emitted, in a context where we can call get_GTOD() */ void update_tsc_params(void) { struct tsc_time_parameters *p = __get_percpu_var(tsc_params); p->version |= 1; wmb(); p->tsc = get_tsc(); p->tsc_freq = get_tsc_freq(); p->gtod = get_GTOD(); wmb(); p->version++; wmb(); } DEFINE_PERCPU(unsigned, current_tsc_version); DEFINE_PERCPU(u64, prev_tsc); /* may be called in any context */ u64 get_trace_timestamp_delta(void) { const struct tsc_time_parameters *p = &__get_percpu_var(tsc_params); unsigned *current_version = &__get_cpu_var(current_tsc_version); u64 prev = __get_cpu_var(prev_tsc); u64 now, ret; /* check the current tsc_params version against the last one we emitted; if the version is odd, then we interrupted the parameters as they were being updated, so just emit a new delta with the old parameters */ if (unlikely(*current_version != p->version && !(p->version & 1))) { /* XXX probably need a loop to deal with p->version changing under our feet */ emit_tsc_freq_record(p); prev = p->tsc; __get_cpu_var(current_tsc_version) = p->version; } now = read_tsc(); ret = now - prev; __get_cpu_var(prev_tsc) = now; return ret; } J