From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Ahern Subject: Re: [PATCH 2/3] perf events: Introduce realtime clock event Date: Fri, 18 Feb 2011 07:39:40 -0700 Message-ID: <4D5E84AC.4040104@cisco.com> References: <1298008433-22911-1-git-send-email-daahern@cisco.com> <1298008433-22911-3-git-send-email-daahern@cisco.com> <1298027641.5226.666.camel@laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: Received: from sj-iport-5.cisco.com ([171.68.10.87]:25817 "EHLO sj-iport-5.cisco.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751314Ab1BROjk (ORCPT ); Fri, 18 Feb 2011 09:39:40 -0500 In-Reply-To: <1298027641.5226.666.camel@laptop> Sender: linux-perf-users-owner@vger.kernel.org List-ID: To: Peter Zijlstra Cc: linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, mingo@elte.hu, acme@ghostprotocols.net, paulus@samba.org On 02/18/11 04:14, Peter Zijlstra wrote: > On Thu, 2011-02-17 at 22:53 -0700, David Ahern wrote: >> The motivation for this event is to convert perf_clock() time stamps >> to wall-clock (gettimeofday()) equivalents, including adjustments made >> by NTP (e.g., for comparing perf events to other log files). > >> This patch is based on the monotonic patch by Arnaldo Carvalho de Melo >> . >> >> (NOTE: Comments from the last review of the timehist patch series >> suggested calling this a monotonic clock. I am not trying to be >> dense here; since gettimeofday maps to realtime clock I think that >> is the better name for it.) > > Well, the idea was to use CLOCK_MONOTONIC, not to call CLOCK_REALTIME > monotonic. > > I'm really not sure why you want CLOCK_REALTIME and I think > CLOCK_MONOTONIC is more useful (I'd argue you want your system logs to > contain both, every admin who's ever had to untangle what happened > during DST switches will agree) I believe CLOCK_MONOTONIC is what perf_clock is tied to -- the timestamps for PERF_SAMPLE_TIME -- so we already have that. Programs that generate time-of-day output are using gettimeofday which is tied to CLOCK_REALTIME. We want to be able to correlate a perf sample to an entry in an applications log file. David > >> @@ -5610,6 +5612,13 @@ static enum hrtimer_restart perf_swevent_hrtimer(struct hrtimer *hrtimer) >> >> perf_sample_data_init(&data, 0); >> data.period = event->hw.last_period; >> + if (event->attr.sample_type & PERF_SAMPLE_RAW) >> + { >> + raw.size = sizeof(u64); >> + raw.data = &event->count; >> + data.raw = &raw; >> + } >> + >> regs = get_irq_regs(); >> >> if (regs && !perf_exclude_event(event, regs)) { > > > Why!? you already keep ->count = ktime_get_real(), so simply reading the > count value will get you the timestamp.. this is superfluous at best. And that is a conundrum I was stuck on for a while. perf record does not sample counters; it only creates sample events. I looked at having perf record sample the clock event, but then I would have to synthesize an event for the output file. Similarly perf record for hardware counters does not show the value of the counter. David > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-perf-users" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html