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

NAME         top

       libpfm_intel_knm - support for Intel Knights Mill core PMU

SYNOPSIS         top

       #include <perfmon/pfmlib.h>

       PMU name: knm
       PMU desc: Intel Kinghts Mill

DESCRIPTION         top

       The library supports the Intel Kinghts Mill core PMU. It should be
       noted that this PMU model only covers each core's PMU and not the
       socket level PMU.

       On Knights Mill, the number of generic counters is 4. There is 4-way
       HyperThreading support.  The pfm_get_pmu_info() function returns the
       maximum number of generic counters in num_cntrs.

MODIFIERS         top

       The following modifiers are supported on Intel Kinghts Mill

       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 any of the 4 hyper-threads at the same time
              assuming hyper-threading is enabled. This is a boolean
              modifier.  This modifier is only available on fixed counters
              (unhalted_reference_cycles, instructions_retired,
              unhalted_core_cycles).  Depending on the underlying kernel
              interface, the event may be programmed on a fixed counter or a
              generic counter, except for unhalted_reference_cycles, in
              which case, this modifier may be ignored or rejected.

OFFCORE_RESPONSE events         top

       Intel Knights Mill provides two offcore_response events. They are

       Those events need special treatment in the performance monitoring
       infrastructure because each event uses an extra register to store
       some settings. Thus, in case multiple offcore_response events are
       monitored simultaneously, the kernel needs to manage the sharing of
       that extra register.

       The offcore_response events are exposed as normal events by the
       library. The extra settings are exposed as regular umasks. The
       library takes care of encoding the events according to the underlying
       kernel interface.

       On Intel Knights Mill, the umasks are divided into 4 categories:
       request, supplier and snoop and average latency. Offcore_response
       event has two modes of operations: normal and average latency.  In
       the first mode, the two offcore_respnse events operate independently
       of each other. The user must provide at least one umask for each of
       the first 3 categories: request, supplier, snoop. In the second mode,
       the two offcore_response events are combined to compute an average
       latency per request type.

       For the normal mode, there is a special supplier (response) umask
       called ANY_RESPONSE. When this umask is used then it overrides any
       supplier and snoop umasks. In other words, users can specify either
       ANY_RESPONSE OR any combinations of supplier + snoops. In case no
       supplier or snoop is specified, the library defaults to using

       For instance, the following are valid event selections:




       But the following is illegal:


       In average latency mode, OFFCORE_RESPONSE_0 must be programmed to
       select the request types of interest, for instance, DMND_DATA_RD, and
       the OUTSTANDING umask must be set and no others. the library will
       enforce that restriction as soon as the OUTSTANDING umask is used.
       Then OFFCORE_RESPONSE_1 must be set with the same request types and
       the ANY_RESPONSE umask. It should be noted that the library encodes
       events independently of each other and therefore cannot verify that
       the requests are matching between the two events.  Example of average
       latency settings:



       The average latency for the request(s) is obtained by dividing the
       counts of OFFCORE_RESPONSE_0 by the count of OFFCORE_RESPONSE_1. The
       ratio is expressed in core cycles.

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
       2020-02-08.  (At that time, the date of the most recent commit that
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                                 March, 2018                       LIBPFM(3)