linux-kernel - Re: [PATCH v1] perf stat: avoid 10ms limit for printing event counts

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Message-ID: <20180327090642.GP13724@tassilo.jf.intel.com>
Date:   Tue, 27 Mar 2018 02:06:42 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] perf stat: avoid 10ms limit for printing event counts

> When running perf stat -I for monitoring e.g. PCIe uncore counters and 
> at the same time profiling some I/O workload by perf record e.g. for 
> cpu-cycles and context switches, it is then possible to build and 
> observe good-enough consolidated CPU/OS/IO(Uncore) performance picture 
> for that workload.

At some point I still hope we can make uncore measurements in 
perf record work. Kan tried at some point to allow multiple
PMUs in a group, but was not successfull. But perhaps we
can sample them from a software event instead.

> 
> The warning on possible runtime overhead is still preserved, however 
> it is only visible when specifying -v option.

I would print it unconditionally. Very few people use -v.

BTW better of course would be to occasionally measure the perf stat 
cpu time and only print the warning if it's above some percentage
of a CPU. But that would be much more work.

Rest looks ok.

-Andi