libpfm_intel_knl(3) — Linux manual page


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

NAME         top

       libpfm_intel_knl - support for Intel Kinghts Landing core PMU

SYNOPSIS         top

       #include <perfmon/pfmlib.h>

       PMU name: knl
       PMU desc: Intel Kinghts Landing

DESCRIPTION         top

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

       On Knights Landing, 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 Landing

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

       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 modifier

       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 Landing provides two offcore_response events. They
       are called OFFCORE_RESPONSE_0 and OFFCORE_RESPONSE_1.

       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 Landing, 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

       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 ANY_RESPONSE.

       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
       2023-12-22.  (At that time, the date of the most recent commit
       that was found in the repository was 2023-09-28.)  If you
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                               July, 2016                      LIBPFM(3)