.. SPDX-License-Identifier: GPL-2.0

============================================================
Intel(R) Speed Select Technology User Guide
============================================================

The Intel(R) Speed Select Technology (Intel(R) SST) provides a powerful new
collection of features that give more granular control over CPU performance.
With Intel(R) SST, one server can be configured for power and performance for a
variety of diverse workload requirements.

Refer to the links below for an overview of the technology:

- https://www.intel.com/content/www/us/en/architecture-and-technology/speed-select-technology-article.html
- https://builders.intel.com/docs/networkbuilders/intel-speed-select-technology-base-frequency-enhancing-performance.pdf

These capabilities are further enhanced in some of the newer generations of
server platforms where these features can be enumerated and controlled
dynamically without pre-configuring via BIOS setup options. This dynamic
configuration is done via mailbox commands to the hardware. One way to enumerate
and configure these features is by using the Intel Speed Select utility.

This document explains how to use the Intel Speed Select tool to enumerate and
control Intel(R) SST features. This document gives example commands and explains
how these commands change the power and performance profile of the system under
test. Using this tool as an example, customers can replicate the messaging
implemented in the tool in their production software.

intel-speed-select configuration tool
======================================

Most Linux distribution packages may include the "intel-speed-select" tool. If not,
it can be built by downloading the Linux kernel tree from kernel.org. Once
downloaded, the tool can be built without building the full kernel.

From the kernel tree, run the following commands::

# cd tools/power/x86/intel-speed-select/
# make
# make install

Getting Help
------------

To get help with the tool, execute the command below::

# intel-speed-select --help

The top-level help describes arguments and features. Notice that there is a
multi-level help structure in the tool. For example, to get help for the feature "perf-profile"::

# intel-speed-select perf-profile --help

To get help on a command, another level of help is provided. For example for the command info "info"::

# intel-speed-select perf-profile info --help

Summary of platform capability
------------------------------
To check the current platform and driver capabilities, execute::

#intel-speed-select --info

For example on a test system::

 # intel-speed-select --info
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 Platform: API version : 1
 Platform: Driver version : 1
 Platform: mbox supported : 1
 Platform: mmio supported : 1
 Intel(R) SST-PP (feature perf-profile) is supported
 TDP level change control is unlocked, max level: 4
 Intel(R) SST-TF (feature turbo-freq) is supported
 Intel(R) SST-BF (feature base-freq) is not supported
 Intel(R) SST-CP (feature core-power) is supported

Intel(R) Speed Select Technology - Performance Profile (Intel(R) SST-PP)
------------------------------------------------------------------------

This feature allows configuration of a server dynamically based on workload
performance requirements. This helps users during deployment as they do not have
to choose a specific server configuration statically.  This Intel(R) Speed Select
Technology - Performance Profile (Intel(R) SST-PP) feature introduces a mechanism
that allows multiple optimized performance profiles per system. Each profile
defines a set of CPUs that need to be online and rest offline to sustain a
guaranteed base frequency. Once the user issues a command to use a specific
performance profile and meet CPU online/offline requirement, the user can expect
a change in the base frequency dynamically. This feature is called
"perf-profile" when using the Intel Speed Select tool.

Number or performance levels
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

There can be multiple performance profiles on a system. To get the number of
profiles, execute the command below::

 # intel-speed-select perf-profile get-config-levels
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 package-0
  die-0
    cpu-0
        get-config-levels:4
 package-1
  die-0
    cpu-14
        get-config-levels:4

On this system under test, there are 4 performance profiles in addition to the
base performance profile (which is performance level 0).

Lock/Unlock status
~~~~~~~~~~~~~~~~~~

Even if there are multiple performance profiles, it is possible that they
are locked. If they are locked, users cannot issue a command to change the
performance state. It is possible that there is a BIOS setup to unlock or check
with your system vendor.

To check if the system is locked, execute the following command::

 # intel-speed-select perf-profile get-lock-status
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 package-0
  die-0
    cpu-0
        get-lock-status:0
 package-1
  die-0
    cpu-14
        get-lock-status:0

In this case, lock status is 0, which means that the system is unlocked.

Properties of a performance level
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To get properties of a specific performance level (For example for the level 0, below), execute the command below::

 # intel-speed-select perf-profile info -l 0
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 package-0
  die-0
    cpu-0
      perf-profile-level-0
        cpu-count:28
        enable-cpu-mask:000003ff,f0003fff
        enable-cpu-list:0,1,2,3,4,5,6,7,8,9,10,11,12,13,28,29,30,31,32,33,34,35,36,37,38,39,40,41
        thermal-design-power-ratio:26
        base-frequency(MHz):2600
        speed-select-turbo-freq:disabled
        speed-select-base-freq:disabled
	...
	...

Here -l option is used to specify a performance level.

If the option -l is omitted, then this command will print information about all
the performance levels. The above command is printing properties of the
performance level 0.

For this performance profile, the list of CPUs displayed by the
"enable-cpu-mask/enable-cpu-list" at the max can be "online." When that
condition is met, then base frequency of 2600 MHz can be maintained. To
understand more, execute "intel-speed-select perf-profile info" for performance
level 4::

 # intel-speed-select perf-profile info -l 4
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 package-0
  die-0
    cpu-0
      perf-profile-level-4
        cpu-count:28
        enable-cpu-mask:000000fa,f0000faf
        enable-cpu-list:0,1,2,3,5,7,8,9,10,11,28,29,30,31,33,35,36,37,38,39
        thermal-design-power-ratio:28
        base-frequency(MHz):2800
        speed-select-turbo-freq:disabled
        speed-select-base-freq:unsupported
	...
	...

There are fewer CPUs in the "enable-cpu-mask/enable-cpu-list". Consequently, if
the user only keeps these CPUs online and the rest "offline," then the base
frequency is increased to 2.8 GHz compared to 2.6 GHz at performance level 0.

Get current performance level
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To get the current performance level, execute::

 # intel-speed-select perf-profile get-config-current-level
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 package-0
  die-0
    cpu-0
        get-config-current_level:0

First verify that the base_frequency displayed by the cpufreq sysfs is correct::

 # cat /sys/devices/system/cpu/cpu0/cpufreq/base_frequency
 2600000

This matches the base-frequency (MHz) field value displayed from the
"perf-profile info" command for performance level 0(cpufreq frequency is in
KHz).

To check if the average frequency is equal to the base frequency for a 100% busy
workload, disable turbo::

# echo 1 > /sys/devices/system/cpu/intel_pstate/no_turbo

Then runs a busy workload on all CPUs, for example::

#stress -c 64

To verify the base frequency, run turbostat::

 #turbostat -c 0-13 --show Package,Core,CPU,Bzy_MHz -i 1

  Package	Core	CPU	Bzy_MHz
		-	-	2600
  0		0	0	2600
  0		1	1	2600
  0		2	2	2600
  0		3	3	2600
  0		4	4	2600
  .		.	.	.


Changing performance level
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To the change the performance level to 4, execute::

 # intel-speed-select -d perf-profile set-config-level -l 4 -o
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 package-0
  die-0
    cpu-0
      perf-profile
        set_tdp_level:success

In the command above, "-o" is optional. If it is specified, then it will also
offline CPUs which are not present in the enable_cpu_mask for this performance
level.

Now if the base_frequency is checked::

 #cat /sys/devices/system/cpu/cpu0/cpufreq/base_frequency
 2800000

Which shows that the base frequency now increased from 2600 MHz at performance
level 0 to 2800 MHz at performance level 4. As a result, any workload, which can
use fewer CPUs, can see a boost of 200 MHz compared to performance level 0.

Changing performance level via BMC Interface
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

It is possible to change SST-PP level using out of band (OOB) agent (Via some
remote management console, through BMC "Baseboard Management Controller"
interface). This mode is supported from the Sapphire Rapids processor
generation. The kernel and tool change to support this mode is added to Linux
kernel version 5.18. To enable this feature, kernel config
"CONFIG_INTEL_HFI_THERMAL" is required. The minimum version of the tool
is "v1.12" to support this feature, which is part of Linux kernel version 5.18.

To support such configuration, this tool can be used as a daemon. Add
a command line option --oob::

 # intel-speed-select --oob
 Intel(R) Speed Select Technology
 Executing on CPU model:143[0x8f]
 OOB mode is enabled and will run as daemon

In this mode the tool will online/offline CPUs based on the new performance
level.

Check presence of other Intel(R) SST features
---------------------------------------------

Each of the performance profiles also specifies whether there is support of
other two Intel(R) SST features (Intel(R) Speed Select Technology - Base Frequency
(Intel(R) SST-BF) and Intel(R) Speed Select Technology - Turbo Frequency (Intel
SST-TF)).

For example, from the output of "perf-profile info" above, for level 0 and level
4:

For level 0::
       speed-select-turbo-freq:disabled
       speed-select-base-freq:disabled

For level 4::
       speed-select-turbo-freq:disabled
       speed-select-base-freq:unsupported

Given these results, the "speed-select-base-freq" (Intel(R) SST-BF) in level 4
changed from "disabled" to "unsupported" compared to performance level 0.

This means that at performance level 4, the "speed-select-base-freq" feature is
not supported. However, at performance level 0, this feature is "supported", but
currently "disabled", meaning the user has not activated this feature. Whereas
"speed-select-turbo-freq" (Intel(R) SST-TF) is supported at both performance
levels, but currently not activated by the user.

The Intel(R) SST-BF and the Intel(R) SST-TF features are built on a foundation
technology called Intel(R) Speed Select Technology - Core Power (Intel(R) SST-CP).
The platform firmware enables this feature when Intel(R) SST-BF or Intel(R) SST-TF
is supported on a platform.

Intel(R) Speed Select Technology Core Power (Intel(R) SST-CP)
---------------------------------------------------------------

Intel(R) Speed Select Technology Core Power (Intel(R) SST-CP) is an interface that
allows users to define per core priority. This defines a mechanism to distribute
power among cores when there is a power constrained scenario. This defines a
class of service (CLOS) configuration.

The user can configure up to 4 class of service configurations. Each CLOS group
configuration allows definitions of parameters, which affects how the frequency
can be limited and power is distributed. Each CPU core can be tied to a class of
service and hence an associated priority. The granularity is at core level not
at per CPU level.

Enable CLOS based prioritization
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To use CLOS based prioritization feature, firmware must be informed to enable
and use a priority type. There is a default per platform priority type, which
can be changed with optional command line parameter.

To enable and check the options, execute::

 # intel-speed-select core-power enable --help
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 Enable core-power for a package/die
	Clos Enable: Specify priority type with [--priority|-p]
		 0: Proportional, 1: Ordered

There are two types of priority types:

- Ordered

Priority for ordered throttling is defined based on the index of the assigned
CLOS group. Where CLOS0 gets highest priority (throttled last).

Priority order is:
CLOS0 > CLOS1 > CLOS2 > CLOS3.

- Proportional

When proportional priority is used, there is an additional parameter called
frequency_weight, which can be specified per CLOS group. The goal of
proportional priority is to provide each core with the requested min., then
distribute all remaining (excess/deficit) budgets in proportion to a defined
weight. This proportional priority can be configured using "core-power config"
command.

To enable with the platform default priority type, execute::

 # intel-speed-select core-power enable
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 package-0
  die-0
    cpu-0
      core-power
        enable:success
 package-1
  die-0
    cpu-6
      core-power
        enable:success

The scope of this enable is per package or die scoped when a package contains
multiple dies. To check if CLOS is enabled and get priority type, "core-power
info" command can be used. For example to check the status of core-power feature
on CPU 0, execute::

 # intel-speed-select -c 0 core-power info
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 package-0
  die-0
    cpu-0
      core-power
        support-status:supported
        enable-status:enabled
        clos-enable-status:enabled
        priority-type:proportional
 package-1
  die-0
    cpu-24
      core-power
        support-status:supported
        enable-status:enabled
        clos-enable-status:enabled
        priority-type:proportional

Configuring CLOS groups
~~~~~~~~~~~~~~~~~~~~~~~

Each CLOS group has its own attributes including min, max, freq_weight and
desired. These parameters can be configured with "core-power config" command.
Defaults will be used if user skips setting a parameter except clos id, which is
mandatory. To check core-power config options, execute::

 # intel-speed-select core-power config --help
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 Set core-power configuration for one of the four clos ids
	Specify targeted clos id with [--clos|-c]
	Specify clos Proportional Priority [--weight|-w]
	Specify clos min in MHz with [--min|-n]
	Specify clos max in MHz with [--max|-m]

For example::

 # intel-speed-select core-power config -c 0
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 clos epp is not specified, default: 0
 clos frequency weight is not specified, default: 0
 clos min is not specified, default: 0 MHz
 clos max is not specified, default: 25500 MHz
 clos desired is not specified, default: 0
 package-0
  die-0
    cpu-0
      core-power
        config:success
 package-1
  die-0
    cpu-6
      core-power
        config:success

The user has the option to change defaults. For example, the user can change the
"min" and set the base frequency to always get guaranteed base frequency.

Get the current CLOS configuration
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To check the current configuration, "core-power get-config" can be used. For
example, to get the configuration of CLOS 0::

 # intel-speed-select core-power get-config -c 0
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 package-0
  die-0
    cpu-0
      core-power
        clos:0
        epp:0
        clos-proportional-priority:0
        clos-min:0 MHz
        clos-max:Max Turbo frequency
        clos-desired:0 MHz
 package-1
  die-0
    cpu-24
      core-power
        clos:0
        epp:0
        clos-proportional-priority:0
        clos-min:0 MHz
        clos-max:Max Turbo frequency
        clos-desired:0 MHz

Associating a CPU with a CLOS group
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To associate a CPU to a CLOS group "core-power assoc" command can be used::

 # intel-speed-select core-power assoc --help
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 Associate a clos id to a CPU
	Specify targeted clos id with [--clos|-c]


For example to associate CPU 10 to CLOS group 3, execute::

 # intel-speed-select -c 10 core-power assoc -c 3
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 package-0
  die-0
    cpu-10
      core-power
        assoc:success

Once a CPU is associated, its sibling CPUs are also associated to a CLOS group.
Once associated, avoid changing Linux "cpufreq" subsystem scaling frequency
limits.

To check the existing association for a CPU, "core-power get-assoc" command can
be used. For example, to get association of CPU 10, execute::

 # intel-speed-select -c 10 core-power get-assoc
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 package-1
  die-0
    cpu-10
      get-assoc
        clos:3

This shows that CPU 10 is part of a CLOS group 3.


Disable CLOS based prioritization
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To disable, execute::

# intel-speed-select core-power disable

Some features like Intel(R) SST-TF can only be enabled when CLOS based prioritization
is enabled. For this reason, disabling while Intel(R) SST-TF is enabled can cause
Intel(R) SST-TF to fail. This will cause the "disable" command to display an error
if Intel(R) SST-TF is already enabled. In turn, to disable, the Intel(R) SST-TF
feature must be disabled first.

Intel(R) Speed Select Technology - Base Frequency (Intel(R) SST-BF)
-------------------------------------------------------------------

The Intel(R) Speed Select Technology - Base Frequency (Intel(R) SST-BF) feature lets
the user control base frequency. If some critical workload threads demand
constant high guaranteed performance, then this feature can be used to execute
the thread at higher base frequency on specific sets of CPUs (high priority
CPUs) at the cost of lower base frequency (low priority CPUs) on other CPUs.
This feature does not require offline of the low priority CPUs.

The support of Intel(R) SST-BF depends on the Intel(R) Speed Select Technology -
Performance Profile (Intel(R) SST-PP) performance level configuration. It is
possible that only certain performance levels support Intel(R) SST-BF. It is also
possible that only base performance level (level = 0) has support of Intel
SST-BF. Consequently, first select the desired performance level to enable this
feature.

In the system under test here, Intel(R) SST-BF is supported at the base
performance level 0, but currently disabled. For example for the level 0::

 # intel-speed-select -c 0 perf-profile info -l 0
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 package-0
  die-0
    cpu-0
      perf-profile-level-0
        ...

        speed-select-base-freq:disabled
	...

Before enabling Intel(R) SST-BF and measuring its impact on a workload
performance, execute some workload and measure performance and get a baseline
performance to compare against.

Here the user wants more guaranteed performance. For this reason, it is likely
that turbo is disabled. To disable turbo, execute::

#echo 1 > /sys/devices/system/cpu/intel_pstate/no_turbo

Based on the output of the "intel-speed-select perf-profile info -l 0" base
frequency of guaranteed frequency 2600 MHz.


Measure baseline performance for comparison
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To compare, pick a multi-threaded workload where each thread can be scheduled on
separate CPUs. "Hackbench pipe" test is a good example on how to improve
performance using Intel(R) SST-BF.

Below, the workload is measuring average scheduler wakeup latency, so a lower
number means better performance::

 # taskset -c 3,4 perf bench -r 100 sched pipe
 # Running 'sched/pipe' benchmark:
 # Executed 1000000 pipe operations between two processes
     Total time: 6.102 [sec]
       6.102445 usecs/op
         163868 ops/sec

While running the above test, if we take turbostat output, it will show us that
2 of the CPUs are busy and reaching max. frequency (which would be the base
frequency as the turbo is disabled). The turbostat output::

 #turbostat -c 0-13 --show Package,Core,CPU,Bzy_MHz -i 1
 Package	Core	CPU	Bzy_MHz
 0		0	0	1000
 0		1	1	1005
 0		2	2	1000
 0		3	3	2600
 0		4	4	2600
 0		5	5	1000
 0		6	6	1000
 0		7	7	1005
 0		8	8	1005
 0		9	9	1000
 0		10	10	1000
 0		11	11	995
 0		12	12	1000
 0		13	13	1000

From the above turbostat output, both CPU 3 and 4 are very busy and reaching
full guaranteed frequency of 2600 MHz.

Intel(R) SST-BF Capabilities
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To get capabilities of Intel(R) SST-BF for the current performance level 0,
execute::

 # intel-speed-select base-freq info -l 0
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 package-0
  die-0
    cpu-0
      speed-select-base-freq
        high-priority-base-frequency(MHz):3000
        high-priority-cpu-mask:00000216,00002160
        high-priority-cpu-list:5,6,8,13,33,34,36,41
        low-priority-base-frequency(MHz):2400
        tjunction-temperature(C):125
        thermal-design-power(W):205

The above capabilities show that there are some CPUs on this system that can
offer base frequency of 3000 MHz compared to the standard base frequency at this
performance levels. Nevertheless, these CPUs are fixed, and they are presented
via high-priority-cpu-list/high-priority-cpu-mask. But if this Intel(R) SST-BF
feature is selected, the low priorities CPUs (which are not in
high-priority-cpu-list) can only offer up to 2400 MHz. As a result, if this
clipping of low priority CPUs is acceptable, then the user can enable Intel
SST-BF feature particularly for the above "sched pipe" workload since only two
CPUs are used, they can be scheduled on high priority CPUs and can get boost of
400 MHz.

Enable Intel(R) SST-BF
~~~~~~~~~~~~~~~~~~~~~~

To enable Intel(R) SST-BF feature, execute::

 # intel-speed-select base-freq enable -a
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 package-0
  die-0
    cpu-0
      base-freq
        enable:success
 package-1
  die-0
    cpu-14
      base-freq
        enable:success

In this case, -a option is optional. This not only enables Intel(R) SST-BF, but it
also adjusts the priority of cores using Intel(R) Speed Select Technology Core
Power (Intel(R) SST-CP) features. This option sets the minimum performance of each
Intel(R) Speed Select Technology - Performance Profile (Intel(R) SST-PP) class to
maximum performance so that the hardware will give maximum performance possible
for each CPU.

If -a option is not used, then the following steps are required before enabling
Intel(R) SST-BF:

- Discover Intel(R) SST-BF and note low and high priority base frequency
- Note the high priority CPU list
- Enable CLOS using core-power feature set
- Configure CLOS parameters. Use CLOS.min to set to minimum performance
- Subscribe desired CPUs to CLOS groups

With this configuration, if the same workload is executed by pinning the
workload to high priority CPUs (CPU 5 and 6 in this case)::

 #taskset -c 5,6 perf bench -r 100 sched pipe
 # Running 'sched/pipe' benchmark:
 # Executed 1000000 pipe operations between two processes
     Total time: 5.627 [sec]
       5.627922 usecs/op
         177685 ops/sec

This way, by enabling Intel(R) SST-BF, the performance of this benchmark is
improved (latency reduced) by 7.79%. From the turbostat output, it can be
observed that the high priority CPUs reached 3000 MHz compared to 2600 MHz.
The turbostat output::

 #turbostat -c 0-13 --show Package,Core,CPU,Bzy_MHz -i 1
 Package	Core	CPU	Bzy_MHz
 0		0	0	2151
 0		1	1	2166
 0		2	2	2175
 0		3	3	2175
 0		4	4	2175
 0		5	5	3000
 0		6	6	3000
 0		7	7	2180
 0		8	8	2662
 0		9	9	2176
 0		10	10	2175
 0		11	11	2176
 0		12	12	2176
 0		13	13	2661

Disable Intel(R) SST-BF
~~~~~~~~~~~~~~~~~~~~~~~

To disable the Intel(R) SST-BF feature, execute::

# intel-speed-select base-freq disable -a


Intel(R) Speed Select Technology - Turbo Frequency (Intel(R) SST-TF)
--------------------------------------------------------------------

This feature enables the ability to set different "All core turbo ratio limits"
to cores based on the priority. By using this feature, some cores can be
configured to get higher turbo frequency by designating them as high priority at
the cost of lower or no turbo frequency on the low priority cores.

For this reason, this feature is only useful when system is busy utilizing all
CPUs, but the user wants some configurable option to get high performance on
some CPUs.

The support of Intel(R) Speed Select Technology - Turbo Frequency (Intel(R) SST-TF)
depends on the Intel(R) Speed Select Technology - Performance Profile (Intel
SST-PP) performance level configuration. It is possible that only a certain
performance level supports Intel(R) SST-TF. It is also possible that only the base
performance level (level = 0) has the support of Intel(R) SST-TF. Hence, first
select the desired performance level to enable this feature.

In the system under test here, Intel(R) SST-TF is supported at the base
performance level 0, but currently disabled::

 # intel-speed-select -c 0 perf-profile info -l 0
 Intel(R) Speed Select Technology
 package-0
  die-0
    cpu-0
      perf-profile-level-0
        ...
        ...
        speed-select-turbo-freq:disabled
        ...
        ...


To check if performance can be improved using Intel(R) SST-TF feature, get the turbo
frequency properties with Intel(R) SST-TF enabled and compare to the base turbo
capability of this system.

Get Base turbo capability
~~~~~~~~~~~~~~~~~~~~~~~~~

To get the base turbo capability of performance level 0, execute::

 # intel-speed-select perf-profile info -l 0
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 package-0
  die-0
    cpu-0
      perf-profile-level-0
        ...
        ...
        turbo-ratio-limits-sse
          bucket-0
            core-count:2
            max-turbo-frequency(MHz):3200
          bucket-1
            core-count:4
            max-turbo-frequency(MHz):3100
          bucket-2
            core-count:6
            max-turbo-frequency(MHz):3100
          bucket-3
            core-count:8
            max-turbo-frequency(MHz):3100
          bucket-4
            core-count:10
            max-turbo-frequency(MHz):3100
          bucket-5
            core-count:12
            max-turbo-frequency(MHz):3100
          bucket-6
            core-count:14
            max-turbo-frequency(MHz):3100
          bucket-7
            core-count:16
            max-turbo-frequency(MHz):3100

Based on the data above, when all the CPUS are busy, the max. frequency of 3100
MHz can be achieved. If there is some busy workload on cpu 0 - 11 (e.g. stress)
and on CPU 12 and 13, execute "hackbench pipe" workload::

 # taskset -c 12,13 perf bench -r 100 sched pipe
 # Running 'sched/pipe' benchmark:
 # Executed 1000000 pipe operations between two processes
     Total time: 5.705 [sec]
       5.705488 usecs/op
         175269 ops/sec

The turbostat output::

 #turbostat -c 0-13 --show Package,Core,CPU,Bzy_MHz -i 1
 Package	Core	CPU	Bzy_MHz
 0		0	0	3000
 0		1	1	3000
 0		2	2	3000
 0		3	3	3000
 0		4	4	3000
 0		5	5	3100
 0		6	6	3100
 0		7	7	3000
 0		8	8	3100
 0		9	9	3000
 0		10	10	3000
 0		11	11	3000
 0		12	12	3100
 0		13	13	3100

Based on turbostat output, the performance is limited by frequency cap of 3100
MHz. To check if the hackbench performance can be improved for CPU 12 and CPU
13, first check the capability of the Intel(R) SST-TF feature for this performance
level.

Get Intel(R) SST-TF Capability
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To get the capability, the "turbo-freq info" command can be used::

 # intel-speed-select turbo-freq info -l 0
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 package-0
  die-0
    cpu-0
      speed-select-turbo-freq
          bucket-0
            high-priority-cores-count:2
            high-priority-max-frequency(MHz):3200
            high-priority-max-avx2-frequency(MHz):3200
            high-priority-max-avx512-frequency(MHz):3100
          bucket-1
            high-priority-cores-count:4
            high-priority-max-frequency(MHz):3100
            high-priority-max-avx2-frequency(MHz):3000
            high-priority-max-avx512-frequency(MHz):2900
          bucket-2
            high-priority-cores-count:6
            high-priority-max-frequency(MHz):3100
            high-priority-max-avx2-frequency(MHz):3000
            high-priority-max-avx512-frequency(MHz):2900
          speed-select-turbo-freq-clip-frequencies
            low-priority-max-frequency(MHz):2600
            low-priority-max-avx2-frequency(MHz):2400
            low-priority-max-avx512-frequency(MHz):2100

Based on the output above, there is an Intel(R) SST-TF bucket for which there are
two high priority cores. If only two high priority cores are set, then max.
turbo frequency on those cores can be increased to 3200 MHz. This is 100 MHz
more than the base turbo capability for all cores.

In turn, for the hackbench workload, two CPUs can be set as high priority and
rest as low priority. One side effect is that once enabled, the low priority
cores will be clipped to a lower frequency of 2600 MHz.

Enable Intel(R) SST-TF
~~~~~~~~~~~~~~~~~~~~~~

To enable Intel(R) SST-TF, execute::

 # intel-speed-select -c 12,13 turbo-freq enable -a
 Intel(R) Speed Select Technology
 Executing on CPU model: X
 package-0
  die-0
    cpu-12
      turbo-freq
        enable:success
 package-0
  die-0
    cpu-13
      turbo-freq
        enable:success
 package--1
  die-0
    cpu-63
      turbo-freq --auto
        enable:success

In this case, the option "-a" is optional. If set, it enables Intel(R) SST-TF
feature and also sets the CPUs to high and low priority using Intel Speed
Select Technology Core Power (Intel(R) SST-CP) features. The CPU numbers passed
with "-c" arguments are marked as high priority, including its siblings.

If -a option is not used, then the following steps are required before enabling
Intel(R) SST-TF:

- Discover Intel(R) SST-TF and note buckets of high priority cores and maximum frequency

- Enable CLOS using core-power feature set - Configure CLOS parameters

- Subscribe desired CPUs to CLOS groups making sure that high priority cores are set to the maximum frequency

If the same hackbench workload is executed, schedule hackbench threads on high
priority CPUs::

 #taskset -c 12,13 perf bench -r 100 sched pipe
 # Running 'sched/pipe' benchmark:
 # Executed 1000000 pipe operations between two processes
     Total time: 5.510 [sec]
       5.510165 usecs/op
         180826 ops/sec

This improved performance by around 3.3% improvement on a busy system. Here the
turbostat output will show that the CPU 12 and CPU 13 are getting 100 MHz boost.
The turbostat output::

 #turbostat -c 0-13 --show Package,Core,CPU,Bzy_MHz -i 1
 Package	Core	CPU	Bzy_MHz
 ...
 0		12	12	3200
 0		13	13	3200
