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authorFenghua Yu <fenghua.yu@intel.com>2020-08-24 12:11:21 -0700
committerBorislav Petkov <bp@suse.de>2020-08-26 17:53:22 +0200
commit29b6bd41ee24f69a85666b9f68d500b382d408fd (patch)
tree8f126a8d5810b3fb15f398e896cf213095a8637f /Documentation/x86
parente48cb1a3fb9165009fe318e1db2fde10d303c1d3 (diff)
x86/resctrl: Enable user to view thread or core throttling mode
Early Intel hardware implementations of Memory Bandwidth Allocation (MBA) could only control bandwidth at the processor core level. This meant that when two processes with different bandwidth allocations ran simultaneously on the same core the hardware had to resolve this difference. It did so by applying the higher throttling value (lower bandwidth) to both processes. Newer implementations can apply different throttling values to each thread on a core. Introduce a new resctrl file, "thread_throttle_mode", on Intel systems that shows to the user how throttling values are allocated, per-core or per-thread. On systems that support per-core throttling, the file will display "max". On newer systems that support per-thread throttling, the file will display "per-thread". AMD confirmed in [1] that AMD bandwidth allocation is already at thread level but that the AMD implementation does not use a memory delay throttle mode. So to avoid confusion the thread throttling mode would be UNDEFINED on AMD systems and the "thread_throttle_mode" file will not be visible. Originally-by: Reinette Chatre <reinette.chatre@intel.com> Signed-off-by: Fenghua Yu <fenghua.yu@intel.com> Signed-off-by: Borislav Petkov <bp@suse.de> Reviewed-by: Reinette Chatre <reinette.chatre@intel.com> Link: https://lkml.kernel.org/r/1598296281-127595-3-git-send-email-fenghua.yu@intel.com Link: [1] https://lore.kernel.org/lkml/18d277fd-6523-319c-d560-66b63ff606b8@amd.com
Diffstat (limited to 'Documentation/x86')
-rw-r--r--Documentation/x86/resctrl_ui.rst18
1 files changed, 16 insertions, 2 deletions
diff --git a/Documentation/x86/resctrl_ui.rst b/Documentation/x86/resctrl_ui.rst
index 5368cedfb530..e59b7b93a9b4 100644
--- a/Documentation/x86/resctrl_ui.rst
+++ b/Documentation/x86/resctrl_ui.rst
@@ -138,6 +138,18 @@ with respect to allocation:
non-linear. This field is purely informational
only.
+"thread_throttle_mode":
+ Indicator on Intel systems of how tasks running on threads
+ of a physical core are throttled in cases where they
+ request different memory bandwidth percentages:
+
+ "max":
+ the smallest percentage is applied
+ to all threads
+ "per-thread":
+ bandwidth percentages are directly applied to
+ the threads running on the core
+
If RDT monitoring is available there will be an "L3_MON" directory
with the following files:
@@ -364,8 +376,10 @@ to the next control step available on the hardware.
The bandwidth throttling is a core specific mechanism on some of Intel
SKUs. Using a high bandwidth and a low bandwidth setting on two threads
-sharing a core will result in both threads being throttled to use the
-low bandwidth. The fact that Memory bandwidth allocation(MBA) is a core
+sharing a core may result in both threads being throttled to use the
+low bandwidth (see "thread_throttle_mode").
+
+The fact that Memory bandwidth allocation(MBA) may be a core
specific mechanism where as memory bandwidth monitoring(MBM) is done at
the package level may lead to confusion when users try to apply control
via the MBA and then monitor the bandwidth to see if the controls are