[PATCH v11 0/8] x86/resctrl: mba_MBps enhancement

Tony Luck
2024-12-06T16:31:53Z

Background
----------

The resctrl filesystem supports a mount option that allows users to
specify a memory bandwidth limit in MiB/s for each domain of a CTRL_MON
group. The underlying implementation uses data collected from the local
memory bandwidth monitoring event for the CTRL_MON group and all of
its MON subgroups as input to a feedback loop that adjusts the memory
bandwidth allocation control percentage up or down to keep the group
within the limit set by the user.

Problem statement
-----------------

Hard coding the local memory bandwidth monitoring event has the following
issues:

1) Some systems may support total memory bandwidth monitoring but
not local. The user cannot use this mount option on such systems.

2) For large workloads that span NUMA domains using local bandwidth
monitoring will not throttle jobs correctly.

3) Users may have a mix of large and small workloads and may want to
use different input events per CTRL_MON group.

Solution
--------

A) Provide a new user interface to choose which event is used for each
CTRL_MON group.

B) Allow systems that only support total memory bandwidth monitoring to
use total bandwidth event.

Changes since v10:
Link: https://lore.kernel.org/all/20241122235832.27498-1-tony.luck@intel.com/

Patch Change
----- ------

2 s/filesystm/filesystem/
Reformat block comment above definition of mba_mbps_default_event using
more of 80 column width

3 s/Update_mba_bw()/update_mba_bw()

Added Reinette's Reviewed-by tag to parts 2-8

N.B. v6.13-rc1 introduced a locking change in commit f1be1788a32e ("block:
model freeze & enter queue as lock for supporting lockdep") that throws
a lockdep splat when mounting the resctrl filesystem (with certain
CONFIG options).

Proposed patches that fix this are here:
Link: https://lore.kernel.org/all/20241206111611.978870-2-ming.lei@redhat.com/
Link: https://lore.kernel.org/all/20241206111611.978870-3-ming.lei@redhat.com/

Babu Moger (1):
x86/resctrl: Introduce resctrl_file_fflags_init() to initialize fflags

Tony Luck (7):
x86/resctrl: Prepare for per-CTRL_MON group mba_MBps control
x86/resctrl: Modify update_mba_bw() to use per CTRL_MON group event
x86/resctrl: Compute memory bandwidth for all supported events
x86/resctrl: Make mba_sc use total bandwidth if local is not supported
x86/resctrl: Add "mba_MBps_event" file to CTRL_MON directories
x86/resctrl: Add write option to "mba_MBps_event" file
x86/resctrl: Document the new "mba_MBps_event" file

Documentation/arch/x86/resctrl.rst | 10 +++
include/linux/resctrl.h | 2 +
arch/x86/kernel/cpu/resctrl/internal.h | 9 ++-
arch/x86/kernel/cpu/resctrl/core.c | 9 ++-
arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 70 +++++++++++++++++
arch/x86/kernel/cpu/resctrl/monitor.c | 94 +++++++++++------------
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 43 +++++++----
7 files changed, 171 insertions(+), 66 deletions(-)

base-commit: 40384c840ea1944d7c5a392e8975ed088ecf0b37
--
2.47.0