LIBPFM(3)                 Linux Programmer's Manual                LIBPFM(3)

NAME         top

       libpfm_intel_nhm - support for Intel Nehalem core PMU

SYNOPSIS         top

       #include <perfmon/pfmlib.h>

       PMU name: nhm
       PMU desc: Intel Nehalem
       PMU name: nhm_ex
       PMU desc: Intel Nehalem EX

DESCRIPTION         top

       The library supports the Intel Nehalem core PMU. It should be noted
       that this PMU model only covers the each core's PMU and not the
       socket level PMU. It is provided separately. Support is provided for
       the Intel Core i7 and Core i5 processors.

MODIFIERS         top

       The following modifiers are supported on Intel Nehalem processors:

       u      Measure at user level which includes privilege levels 1, 2, 3.
              This corresponds to PFM_PLM3.  This is a boolean modifier.

       k      Measure at kernel level which includes privilege level 0. This
              corresponds to PFM_PLM0.  This is a boolean modifier.

       i      Invert the meaning of the event. The counter will now count
              cycles in which the event is not occurring. This is a boolean

       e      Enable edge detection, i.e., count only when there is a state
              transition from no occurrence of the event to at least one
              occurrence. This modifier must be combined with a counter mask
              modifier (m) with a value greater or equal to one.  This is a
              boolean modifier.

       c      Set the counter mask value. The mask acts as a threshold. The
              counter will count the number of cycles in which the number of
              occurrences of the event is greater or equal to the threshold.
              This is an integer modifier with values in the range [0:255].

       t      Measure on both threads at the same time assuming hyper-
              threading is enabled. This is a boolean modifier.

       ldlat  Pass a latency threshold to the
              MEM_INST_RETIRED:LATENCY_ABOVE_THRESHOLD event.  This is an
              integer attribute that must be in the range [3:65535]. It is
              required for this event.  Note that the event must be used
              with precise sampling (PEBS).

OFFCORE_RESPONSE event         top

       The library is able to encode the OFFCORE_RESPONSE_0 event. This is a
       special event because it needs a second MSR (0x1a6) to be programmed
       for the event to count properly. Thus two values are necessary. The
       first value can be programmed on any of the generic counters. The
       second value goes into the dedicated MSR (0x1a6).

       The OFFCORE_RESPONSE event is exposed as a normal event with several
       umasks which are divided in two groups: request and response. The
       user must provide at least one umask from each group.  For instance,

       When using pfm_get_event_encoding(), two 64-bit values are returned.
       The first value corresponds to what needs to be programmed into any
       of the generic counters. The second value must be programmed into the
       dedicated MSR (0x1a6).

       When using an OS-specific encoding routine, the way the event is
       encoded is OS specific. Refer to the corresponding man page for more

AUTHORS         top

       Stephane Eranian <>

COLOPHON         top

       This page is part of the perfmon2 (a performance monitoring library)
       project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug report for this
       manual page, send it to  This
       page was obtained from the project's upstream Git repository
       ⟨git:// perfmon2-libpfm4⟩ on
       2018-04-30.  (At that time, the date of the most recent commit that
       was found in the repository was 2018-04-26.)  If you discover any
       rendering problems in this HTML version of the page, or you believe
       there is a better or more up-to-date source for the page, or you have
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       (which is not part of the original manual page), send a mail to

                               September, 2009                     LIBPFM(3)