What:           /sys/bus/event_source/devices/cpu.../rdpmc
Date:           November 2011
KernelVersion:  3.10
Contact:        Linux kernel mailing list linux-kernel@vger.kernel.org
Description:    The /sys/bus/event_source/devices/cpu.../rdpmc attribute
                is used to show/manage if rdpmc instruction can be
                executed in user space. This attribute supports 3 numbers.
                - rdpmc = 0
                user space rdpmc is globally disabled for all PMU
                counters.
                - rdpmc = 1
                user space rdpmc is globally enabled only in event mmap
                ioctl called time window. If the mmap region is unmapped,
                user space rdpmc is disabled again.
                - rdpmc = 2
                user space rdpmc is globally enabled for all PMU
                counters.

                In the Intel platforms supporting counter level's user
                space rdpmc disable feature (CPUID.23H.EBX[2] = 1), the
                meaning of 3 numbers is extended to
                - rdpmc = 0
                global user space rdpmc and counter level's user space
                rdpmc of all counters are both disabled.
                - rdpmc = 1
                No changes on behavior of global user space rdpmc.
                counter level's rdpmc of system-wide events is disabled
                but counter level's rdpmc of non-system-wide events is
                enabled.
                - rdpmc = 2
                global user space rdpmc and counter level's user space
                rdpmc of all counters are both enabled unconditionally.

                The default value of rdpmc is 1.

                Please notice:
                - global user space rdpmc's behavior would change
                immediately along with the rdpmc value's change,
                but the behavior of counter level's user space rdpmc
                won't take effect immediately until the event is
                reactivated or recreated.
                - The rdpmc attribute is global, even for x86 hybrid
                platforms. For example, changing cpu_core/rdpmc will
                also change cpu_atom/rdpmc.