Re: Enabling RDPMC in user space by default

From: Andi Kleen (ak_at_suse.de)
Date: 11/29/05

  • Next message: Parag Warudkar: "Re: PowerBook5,8 - TrackPad update" 
    Date:	Tue, 29 Nov 2005 17:17:00 +0100
To: Mikael Pettersson <mikpe@csd.uu.se>

    > PMC0 stops being a cycle counter as soon as any real driver
    > (not the NMI watchdog) takes over the hardware, such as oprofile,
    > perfmon2, or perfctr. So user-space cannot rely on the semantics

    They're wrong then. oprofile shouldn't disable the NMI
    watchdog. If it does it's broken and needs to be fixed.

    > Disabling user-space RDTSC (setting CR4.TSD) seems evil and pointless.
    > At least some users of it (the perfctr library and I hope eventually
    > also perfmon2) do use it in an SMP-safe manner (through special
    > user/kernel protocols).

    How do you handle P state changes? I don't think it can be safely
    used in user space.

    -Andi
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