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Documentation/x86: Rename resctrl_ui.rst and add two errata to the file

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Intel Memory Bandwidth Monitoring (MBM) counters may report system
memory bandwidth incorrectly on some Intel processors. This is reported
in documented in erratum SKX99, erratum BDF102 and in the RDT reference
manual, see Documentation/x86/index.rst.

To work around the errata, MBM total and local readings are corrected
using a correction factor table.

Since the correction factor table is not publicly documented anywhere,
document the table and the errata in Documentation/x86/resctrl.rst for
future reference.

 [ bp: Move web links to the doc, massage. ]

Suggested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lkml.kernel.org/r/20201014004927.1839452-2-fenghua.yu@intel.com
This commit is contained in:
Fenghua Yu 2020-10-14 00:49:26 +00:00 committed by Borislav Petkov
parent 3650b228f8
commit d1b22e36e3
2 changed files with 94 additions and 1 deletions
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2
Documentation/x86/index.rst
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@ -27,7 +27,7 @@ x86-specific Documentation
pti
mds
microcode
resctrl_ui
resctrl
tsx_async_abort
usb-legacy-support
i386/index

93
Documentation/x86/resctrl_ui.rst → Documentation/x86/resctrl.rst
View File

@ -1209,3 +1209,96 @@ View the llc occupancy snapshot::
# cat /sys/fs/resctrl/p1/mon_data/mon_L3_00/llc_occupancy
11234000
Intel RDT Errata
================
Intel MBM Counters May Report System Memory Bandwidth Incorrectly
-----------------------------------------------------------------
Errata SKX99 for Skylake server and BDF102 for Broadwell server.
Problem: Intel Memory Bandwidth Monitoring (MBM) counters track metrics
according to the assigned Resource Monitor ID (RMID) for that logical
core. The IA32_QM_CTR register (MSR 0xC8E), used to report these
metrics, may report incorrect system bandwidth for certain RMID values.
Implication: Due to the errata, system memory bandwidth may not match
what is reported.
Workaround: MBM total and local readings are corrected according to the
following correction factor table:
+---------------+---------------+---------------+-----------------+
|core count |rmid count |rmid threshold |correction factor|
+---------------+---------------+---------------+-----------------+
|1 |8 |0 |1.000000 |
+---------------+---------------+---------------+-----------------+
|2 |16 |0 |1.000000 |
+---------------+---------------+---------------+-----------------+
|3 |24 |15 |0.969650 |
+---------------+---------------+---------------+-----------------+
|4 |32 |0 |1.000000 |
+---------------+---------------+---------------+-----------------+
|6 |48 |31 |0.969650 |
+---------------+---------------+---------------+-----------------+
|7 |56 |47 |1.142857 |
+---------------+---------------+---------------+-----------------+
|8 |64 |0 |1.000000 |
+---------------+---------------+---------------+-----------------+
|9 |72 |63 |1.185115 |
+---------------+---------------+---------------+-----------------+
|10 |80 |63 |1.066553 |
+---------------+---------------+---------------+-----------------+
|11 |88 |79 |1.454545 |
+---------------+---------------+---------------+-----------------+
|12 |96 |0 |1.000000 |
+---------------+---------------+---------------+-----------------+
|13 |104 |95 |1.230769 |
+---------------+---------------+---------------+-----------------+
|14 |112 |95 |1.142857 |
+---------------+---------------+---------------+-----------------+
|15 |120 |95 |1.066667 |
+---------------+---------------+---------------+-----------------+
|16 |128 |0 |1.000000 |
+---------------+---------------+---------------+-----------------+
|17 |136 |127 |1.254863 |
+---------------+---------------+---------------+-----------------+
|18 |144 |127 |1.185255 |
+---------------+---------------+---------------+-----------------+
|19 |152 |0 |1.000000 |
+---------------+---------------+---------------+-----------------+
|20 |160 |127 |1.066667 |
+---------------+---------------+---------------+-----------------+
|21 |168 |0 |1.000000 |
+---------------+---------------+---------------+-----------------+
|22 |176 |159 |1.454334 |
+---------------+---------------+---------------+-----------------+
|23 |184 |0 |1.000000 |
+---------------+---------------+---------------+-----------------+
|24 |192 |127 |0.969744 |
+---------------+---------------+---------------+-----------------+
|25 |200 |191 |1.280246 |
+---------------+---------------+---------------+-----------------+
|26 |208 |191 |1.230921 |
+---------------+---------------+---------------+-----------------+
|27 |216 |0 |1.000000 |
+---------------+---------------+---------------+-----------------+
|28 |224 |191 |1.143118 |
+---------------+---------------+---------------+-----------------+
If rmid > rmid threshold, MBM total and local values should be multiplied
by the correction factor.
See:
1. Erratum SKX99 in Intel Xeon Processor Scalable Family Specification Update:
http://web.archive.org/web/20200716124958/https://www.intel.com/content/www/us/en/processors/xeon/scalable/xeon-scalable-spec-update.html
2. Erratum BDF102 in Intel Xeon E5-2600 v4 Processor Product Family Specification Update:
http://web.archive.org/web/20191125200531/https://www.intel.com/content/dam/www/public/us/en/documents/specification-updates/xeon-e5-v4-spec-update.pdf
3. The errata in Intel Resource Director Technology (Intel RDT) on 2nd Generation Intel Xeon Scalable Processors Reference Manual:
https://software.intel.com/content/www/us/en/develop/articles/intel-resource-director-technology-rdt-reference-manual.html
for further information.