[PATCH V4 0/4] x86/resctrl: Enable user to view and select thread throttling mode

[Reinette Chatre]

V3 upstream submission available from:
https://lore.kernel.org/lkml/cover.1588808537.git.reinette.chatre@xxxxxxxxx

Patches apply against x86/cache branch of tip repo at
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git

Changes since V3:
- Maintain the thread throttling mode as a property ("arch_throttle_mode")
  of the memory bandwidth allocation resource
  instead of calling a function that queries the system's model each time
  this information is needed. Use this new property generically throughout
  with the goal of being independent of architecture. (Babu)
- Remove "intel" from thread_throttle_mode_init_intel_rw() and
  thread_throttle_mode_init_intel_ro() in anticipation of usage by other
  architectures.
- Use function parameter to update_mba_cfg() directly instead of having
  local variable point to it. (Fenghua)
- Remove unnecessary additional check whether platform supports feature
  from the "thread_throttle_mode" callback. The file will only be
  accessible on platforms that support the feature.
- Rework commit message of first patch to be more complete regarding
  support of all architectures after incorporating AMD feedback.
- View the thread throttle mode with rdtgroup mutex held since it is using
  cached information that may be changed concurrently.
- Remove unnecessary empty line. (Babu)

V2 upstream submission available from:
https://lore.kernel.org/lkml/cover.1586801373.git.reinette.chatre@xxxxxxxxx

Changes since V2:
- Rebase on top of recently merged series "x86/resctrl: Support wider
  MBM counters". Small change needed to take into account
  asm/resctrl_sched.h -> asm/resctrl.h name change.
- Fix rST formatting of documentation (resctrl_ui.rst) describing
  new "thread_throttle_mode" resctrl file.
- Use boot_cpu_has() instead of static_cpu_has() when determining what
  to display to user (slow path).

V1 upstream submission available from:
https://lore.kernel.org/lkml/cover.1585765499.git.reinette.chatre@xxxxxxxxx

A notable change since V1 is the inclusion of two additional patches from
Fenghua Yu that introduce the new per-thread MBA feature. These changes are
added to this series because they are small and closely related to the
original submission. The per-thread MBA feature is a hardware advancement
that requires no software interface changes. The patches added just enumerate
the feature and expose it to userspace by showing "per-thread" in the new
resctrl file "thread_throttle_mode" to help user applications fine tune
performance.

There are currently a few resctrl changes outstanding for upstream inclusion.
To support their consideration all outstanding resctrl patches can be
viewed at https://github.com/rchatre/linux.git (branch resctrl/next)

Changes since V1 (also documented within patches to which they apply):
- Rebased on top of James Morse's CDP fix
(https://lore.kernel.org/lkml/20200221162105.154163-1-james.morse@xxxxxxx)
- Remove RF_UNINITIALIZED (having uninitialized be represented with ones
  creates too much confusion), replace with an explicit check of rft->fflags
  in rdtgroup_add_files() (Fenghua Yu)
- Rename MBA_THREAD_THROTTLE_MODE to MBA_THROTTLE_MODE_MASK to clarify its
  use as a mask (Tony Luck)
- Introduce explicit MBA_THROTTLE_MODE_MAX instead of implying it is the
  opposite of min and use these values (min and max) explicitly whenever
  testing/setting the throttle mode value (Tony Luck)
- Add __init attribute to thread_throttle_mode_init_intel_rw() and
  thread_throttle_mode_init_intel_ro() since they are only needed during
  initialization (Fenghua Yu)
- Remove MBA_CFG MSR reads and error checking so that the patch is simpler
  and easier to review (Fenghua Yu)
- Ensure CPU hotplug lock is taken when writing register on multiple CPUs (Fenghua Yu)
- Use CPU mask already maintained as part of domains to determine which
  CPUs to update MBA register on (Fenghua Yu)
- Maintain MBA configuration register contents to support use case when not
  all CPUs of a package are online when configuration is set from user
  space
- Use seq_puts() instead of seq_printf() when simple strings are printed
- Set MBA configuration to default when resctrl is unmounted
- Complete rewrite of "thread_throttle_mode" documentation (Tony Luck)
- Remove unnecessary checks on user input (Andy Shevchenko)
- Change code style surrounding usage of sysfs_match_string() (Andy Shevchenko)

>From V1 submission:

The first patch in this series introduces a new resctrl file,
"thread_throttle_mode", on Intel systems that exposes to the
user how per-thread values are allocated to a core. This is added in
support of newer Intel systems that can be configured to allocate
either maximum or minimum throttling of the per-thread CLOS values
to the core.

Details about the feature can be found in the commit description and
in Chapter 9 of the most recent Intel ISE available from
https://software.intel.com/sites/default/files/managed/c5/15/architecture-instruction-set-extensions-programming-reference.pdf

The first patch parses user input with the appropriate sysfs API that has
not previously been used in resctrl. The second (later in the fourth) patch is
added as a subsequent cleanup that switches existing resctrl string parsing
code to also use this appropriate API.



Fenghua Yu (2):
  x86/resctrl: Enumerate per-thread MBA
  x86/resctrl: Enable per-thread MBA

Reinette Chatre (2):
  x86/resctrl: Enable user to view and select thread throttling mode
  x86/resctrl: Use appropriate API for strings terminated by newline

 Documentation/x86/resctrl_ui.rst       |  22 ++-
 arch/x86/include/asm/cpufeatures.h     |   1 +
 arch/x86/kernel/cpu/cpuid-deps.c       |   1 +
 arch/x86/kernel/cpu/resctrl/core.c     |  57 ++++++
 arch/x86/kernel/cpu/resctrl/internal.h |  49 ++++-
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 239 +++++++++++++++++++++++--
 arch/x86/kernel/cpu/scattered.c        |   1 +
 7 files changed, 346 insertions(+), 24 deletions(-)

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2.21.0