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Date:   Fri, 31 Jul 2020 20:05:39 +0200
From:   peterz@infradead.org
To:     Andi Kleen <ak@linux.intel.com>
Cc:     Jiri Olsa <jolsa@redhat.com>, David Ahern <dsahern@gmail.com>,
        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>,
        =?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
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On Fri, Jul 31, 2020 at 08:36:12AM -0700, Andi Kleen wrote:
> > yep, we have a customer that needs to compare data from multiple servers
> 
> It's also needed to correlate over different guests on the same machine.
> This is an important use case.

Both these cases you want to sync up CLOCK_MONOTONIC, using walltime is
just utterly misguided.

What happens if the servers have (per accident or otherwise) different
DST settings, or someone does a clock_setttime() for giggles.

All you really want is a clock that runs at the same rate but is not
subject to random jumps and user foibles.