From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Ahern Subject: Re: [PATCH 3/6] perf record: add time-of-day option Date: Tue, 01 Mar 2011 09:45:27 -0700 Message-ID: <4D6D22A7.6000000@cisco.com> References: <1298865151-23656-1-git-send-email-daahern@cisco.com> <1298865151-23656-4-git-send-email-daahern@cisco.com> <1298989751.5226.863.camel@laptop> <4D6D0438.2090901@cisco.com> <1298993714.5226.871.camel@laptop> <4D6D13C6.5020807@cisco.com> <1298995250.5226.882.camel@laptop> <4D6D1A4C.1090009@cisco.com> <1298997435.5226.890.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]:2679 "EHLO sj-iport-5.cisco.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753195Ab1CAQpM (ORCPT ); Tue, 1 Mar 2011 11:45:12 -0500 In-Reply-To: <1298997435.5226.890.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, acme@ghostprotocols.net, mingo@elte.hu, fweisbec@gmail.com, paulus@samba.org, tglx@linutronix.de On 03/01/2011 09:37 AM, Peter Zijlstra wrote: > On Tue, 2011-03-01 at 09:09 -0700, David Ahern wrote: >> >> I did not code it create samples of a realtime-clock event; I coded it >> to add an event to the stream on demand -- whatever event the fd is >> tied to. >> >> > Well yes, but aside from you and the realtime clock stuff, who'd ever > want to do this particular thing? One example would be a system watchdog that decided for some reason or another to force an event sample because of some event it detected. > > I'd much rather expose the whole > local_clock()/perf_clock()/trace_clock() (should all be the same anyway) > as a posix clock using CLOCK_TRACING or whatever would be an appropriate > name. > > [ Since the whole thing is NMI safe it should be well possible to make a > VDSO version as well. ] > > Anyway, once its visible as a posix clock you can sync up from > userspace. And this clock is indeed wanted for other things too, like > user-space tracing etc. > And for some silly reason I sense a time trap here (pun intended) ..... So your pushback is: 1. throw out the realtime-clock event patch, 2. add a new CLOCK_TRACING type to clock_gettime with VDSO hook, 3. and use a synthesized event from userspace for snapshotting perf_clock to time-of-day -- similar to what I have now, but one that will guarantee a time-of-day to perf_clock correlation (versus the current one which hopes that perf_clock is the monotonic clock). David