bionic (3) libpfm_intel_knl.3.gz

NAME

       libpfm_intel_knl - support for Intel Kinghts Landing core PMU

SYNOPSIS

       #include <perfmon/pfmlib.h>

       PMU name: knl
       PMU desc: Intel Kinghts Landing

DESCRIPTION

       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

       The following modifiers are supported on Intel Kinghts Landing 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 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

       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 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 ANY_RESPONSE.

       For instance, the following are valid event selections:

       OFFCORE_RESPONSE_0:DMND_DATA_RD:ANY_RESPONSE

       OFFCORE_RESPONSE_0:ANY_REQUEST

       OFFCORE_RESPONSE_0:ANY_RFO:DDR_NEAR

       But the following is illegal:

       OFFCORE_RESPONSE_0:ANY_RFO:DDR_NEAR:ANY_RESPONSE

       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:

       OFFCORE_RESPONSE_0:DMND_DATA_RD:OUTSTANDING+OFFCORE_RESPONSE_1:DMND_DATA_RD:ANY_RESPONSE

       OFFCORE_RESPONSE_0:ANY_REQUEST:OUTSTANDING+OFFCORE_RESPONSE_1:ANY_REQUEST:ANY_RESPONSE

       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

       Stephane Eranian <eranian@gmail.com>

                                                   July, 2016                                          LIBPFM(3)