Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 31 Jul 2020 19:20:06 +0200
From:   peterz@infradead.org
To:     David Ahern <dsahern@gmail.com>
Cc:     Jiri Olsa <jolsa@kernel.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Michael Petlan <mpetlan@redhat.com>,
        Ian Rogers <irogers@google.com>,
        Andi Kleen <ak@linux.intel.com>,
        =?iso-8859-1?Q?Genevi=E8ve?= Bastien <gbastien@versatic.net>,
        Wang Nan <wangnan0@huawei.com>,
        Jeremie Galarneau <jgalar@efficios.com>
Subject: Re: [PATCH 0/6] perf tools: Add wallclock time conversion support
Message-ID: <20200731172006.GJ2638@hirez.programming.kicks-ass.net>
References: <20200730213950.1503773-1-jolsa@kernel.org>
 <20200730221423.GH2638@hirez.programming.kicks-ass.net>
 <a59b833f-bcb7-3d1b-6e0c-8758b47b93a3@gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <a59b833f-bcb7-3d1b-6e0c-8758b47b93a3@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Jul 30, 2020 at 07:21:54PM -0600, David Ahern wrote:
> On 7/30/20 4:14 PM, peterz@infradead.org wrote:
> > On Thu, Jul 30, 2020 at 11:39:44PM +0200, Jiri Olsa wrote:
> > 
> >> The patchset is adding the ability to display TOD/wallclock timestamp
> >> in 'perf script' output and in 'perf data convert --to-ctf' subcommand,
> >> so the converted CTF data contain TOD/wallclock timestamps.
> > 
> > But why? Wallclock is a horrible piece of crap. Why would you want to do
> > this?
> > 
> 
> Same reason I brought this up 9+ years ago: userspace lives on
> time-of-day, and troubleshooting is based on correlating timestamps from
> multiple sources. To correlate a perf event to syslog or an application
> log, we need time-of-day.

You need a sync'ed CLOCK_MONOTONIC for that, CLOCK_REALTIME 'aka'
wallclock is a trainwreck, you don't ever want that.