LIBPFM(3) Linux Programmer's Manual LIBPFM(3)NAMElibpfm_intel_snb - support for Intel Sandy Bridge core PMU
SYNOPSIS
#include <perfmon/pfmlib.h>
PMU name: snb
PMU desc: Intel Sandy Bridge
PMU name: snb_ep
PMU desc: Intel Sandy Bridge EP
DESCRIPTION
The library supports the Intel Sandy Bridge core PMU. It should be
noted that this PMU model only covers each core's PMU and not the
socket level PMU. For that refer to the Sandy Bridge uncore PMU sup‐
port.
On Sandy Bridge, the number of generic counters depends on the Hyper‐
threading (HT) mode. When HT is on, then only 4 generic counters are
available. When HT is off, then 8 generic counters are available. The
pfm_get_pmu_info() function returns the maximum number of generic coun‐
ters in num_cntrs.
MODIFIERS
The following modifiers are supported on Intel Sandy Bridge 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 both threads at the same time assuming hyper-thread‐
ing is enabled. This is a boolean modifier.
ldlat Pass a latency threshold to the
MEM_TRANS_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 events
Intel Sandy Bridge provides two offcore_response events, like Intel
Westmere. They are called OFFCORE_RESPONSE_0 and OFFCORE_RESPONSE_1.
Those events need special treatment in the performance monitoring in‐
frastructure 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 a 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 Sandy Bridge, the umasks are divided into three categories:
request, supplier and snoop. The user must provide at least one umask
for each category. The categories are shown in the umask descriptions.
There is also the special 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:LLC_HITM:SNOOP_ANY
But the following are illegal:
OFFCORE_RESPONSE_0:ANY_RFO:LLC_HITM:ANY_RESPONSE
OFFCORE_RESPONSE_0:ANY_RFO:LLC_HITM:SNOOP_ANY:ANY_RESPONSE
SEE ALSOlibpfm_snb_unc(3)AUTHORS
Stephane Eranian <eranian@gmail.com>
January, 2011 LIBPFM(3)
