Messages in this thread | | | Date | Tue, 7 Feb 2017 11:54:12 +0100 | From | Borislav Petkov <> | Subject | 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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