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Re: [RFC PATCH] perf/stat: Add --disable-hwdt

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On Tue, Feb 07, 2017 at 08:25:12AM +0100, Ingo Molnar wrote:
> But there's only so much we can do about that, the /proc/sys API is fundamentally 
> lossy in that regard. We'd have to add much more involved kernel support to 
> guarantee that the watchdog state is restored.

So I think doing all this is meh but I guess I probably should do it
just so that we're thorough.

> A way to do it would be create a new /proc/sys/kernel/watchdog_disable_file that 
> disables that watchdog while it's _open_. When a task exits and the kernel 
> automatically closes the file, the watchdog is re-enabled again. (Or the process 
> itself can close the file too.)
> 
> This method would also nest properly and would handle multi-processes races 
> correctly: for example if a script runs perf as root, and root uses 'perf top', 
> the two should not race and the hardware watchdog should not end up being 
> disabled...

Hmm, so I don't like the aspect of adding a /proc file just for that.

Can we do something with sys_perf_event_open(..., flags) instead and
pass in a new flag that says:

PERF_FLAG_SHOO_COUNTER_USERS

or so which would go and turn off HW WDT (and possibly future things
using counters) while we're running a session?

The name should be generic enough so that we can use it for future
temporary disabling of things while a perf session runs.

Then on perf's exit path - I see there are a bunch of _destroy() things
being called when events are disappearing - we'd reenable stuff again
based on that flag.

This way we're clean in userspace and have the maximum control over
everything since we're in the kernel.

From a quick staring, there's PERF_FLAG_FD_CLOEXEC which is a good
example for something like that. It doesn't do what I'd like to do but I
think I should model this in a similar fashion.

Thoughts?

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

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[RFC PATCH] perf/stat: Add --disable-hwdt Borislav Petkov <bp@alien8.de> - 2017-02-06 13:20 +0100
  Re: [RFC PATCH] perf/stat: Add --disable-hwdt Ingo Molnar <mingo@kernel.org> - 2017-02-06 13:30 +0100
    Re: [RFC PATCH] perf/stat: Add --disable-hwdt Borislav Petkov <bp@alien8.de> - 2017-02-06 13:50 +0100
      Re: [RFC PATCH] perf/stat: Add --disable-hwdt Borislav Petkov <bp@alien8.de> - 2017-02-06 13:50 +0100
        Re: [RFC PATCH] perf/stat: Add --disable-hwdt Robert Richter <rric@kernel.org> - 2017-02-06 14:20 +0100
          Re: [RFC PATCH] perf/stat: Add --disable-hwdt Borislav Petkov <bp@alien8.de> - 2017-02-06 14:30 +0100
            Re: [RFC PATCH] perf/stat: Add --disable-hwdt Ingo Molnar <mingo@kernel.org> - 2017-02-07 08:30 +0100
              Re: [RFC PATCH] perf/stat: Add --disable-hwdt Borislav Petkov <bp@alien8.de> - 2017-02-07 12:00 +0100
                Re: [RFC PATCH] perf/stat: Add --disable-hwdt Borislav Petkov <bp@alien8.de> - 2017-02-07 16:10 +0100
                Re: [RFC PATCH] perf/stat: Add --disable-hwdt Borislav Petkov <bp@alien8.de> - 2017-02-11 18:10 +0100
                Re: [RFC PATCH] perf/stat: Add --disable-hwdt Ingo Molnar <mingo@kernel.org> - 2017-02-11 19:00 +0100
                Re: [RFC PATCH] perf/stat: Add --disable-hwdt Borislav Petkov <bp@alien8.de> - 2017-02-11 19:40 +0100
                Re: [RFC PATCH] perf/stat: Add --disable-hwdt Ingo Molnar <mingo@kernel.org> - 2017-02-11 21:50 +0100
          Re: [RFC PATCH] perf/stat: Add --disable-hwdt Vince Weaver <vince@deater.net> - 2017-02-06 15:30 +0100
            Re: [RFC PATCH] perf/stat: Add --disable-hwdt Borislav Petkov <bp@alien8.de> - 2017-02-06 18:10 +0100
        Re: [RFC PATCH] perf/stat: Add --disable-hwdt Borislav Petkov <bp@alien8.de> - 2017-02-07 02:10 +0100
          [PATCH 1/2] tools/lib/api/fs: Add procfs int read/write helpers Borislav Petkov <bp@alien8.de> - 2017-02-07 02:10 +0100
            Re: [PATCH 1/2] tools/lib/api/fs: Add procfs int read/write helpers Arnaldo Carvalho de Melo <acme@kernel.org> - 2017-02-07 02:50 +0100
              Re: [PATCH 1/2] tools/lib/api/fs: Add procfs int read/write helpers Borislav Petkov <bp@alien8.de> - 2017-02-07 11:40 +0100
                Re: [PATCH 1/2] tools/lib/api/fs: Add procfs int read/write helpers Borislav Petkov <bp@alien8.de> - 2017-02-07 16:10 +0100
                Re: [PATCH 1/2] tools/lib/api/fs: Add procfs int read/write helpers Arnaldo Carvalho de Melo <acme@kernel.org> - 2017-02-07 16:40 +0100
                Re: [PATCH 1/2] tools/lib/api/fs: Add procfs int read/write helpers Arnaldo Carvalho de Melo <acme@kernel.org> - 2017-02-07 16:10 +0100
          [PATCH 2/2] perf stat: Disable HW watchdog around a perf stat session Borislav Petkov <bp@alien8.de> - 2017-02-07 02:20 +0100
            Re: [PATCH 2/2] perf stat: Disable HW watchdog around a perf stat  session Arnaldo Carvalho de Melo <acme@kernel.org> - 2017-02-07 02:50 +0100
      Re: [RFC PATCH] perf/stat: Add --disable-hwdt Ingo Molnar <mingo@kernel.org> - 2017-02-06 13:50 +0100

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