lkml.org 
[lkml]   [2020]   [Oct]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v3 1/2] Documentation: x86: Rename resctrl_ui.rst and add two errata to the file
Date
Intel Memory Bandwidth Monitoring (MBM) counters may report system
memory bandwidth incorrectly on some Intel processors. The errata are
reported in erratum SKX99 [1], erratum BDF102 [2] and RDT reference
manual [3].

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,
the table and the errata are documented in Documentation/x86/resctrl.rst
for future reference. The resctrl.rst file is renamed from
Documentation/x86/resctrl_ui.rst because the file won't contain user
interface only anymore.

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

Suggested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
---
Change Log:
v3:
- Remove unnecessary conf.py change in patch 1 (Randy).

v2:
- Document the correction factor table and errata in resctrl.rst (Boris).
- Change the documentation URLs to stable archive.org (Tony).

Documentation/x86/index.rst | 2 +-
.../x86/{resctrl_ui.rst => resctrl.rst} | 82 +++++++++++++++++++
2 files changed, 83 insertions(+), 1 deletion(-)
rename Documentation/x86/{resctrl_ui.rst => resctrl.rst} (92%)

diff --git a/Documentation/x86/index.rst b/Documentation/x86/index.rst
index 265d9e9a093b..49d2fd9f0e5b 100644
--- a/Documentation/x86/index.rst
+++ b/Documentation/x86/index.rst
@@ -25,7 +25,7 @@ x86-specific Documentation
pti
mds
microcode
- resctrl_ui
+ resctrl
tsx_async_abort
usb-legacy-support
i386/index
diff --git a/Documentation/x86/resctrl_ui.rst b/Documentation/x86/resctrl.rst
similarity index 92%
rename from Documentation/x86/resctrl_ui.rst
rename to Documentation/x86/resctrl.rst
index e59b7b93a9b4..8b8ca6de5e1f 100644
--- a/Documentation/x86/resctrl_ui.rst
+++ b/Documentation/x86/resctrl.rst
@@ -1209,3 +1209,85 @@ 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: The kernel works around the errata.
+
+MBM total and local readings are corrected by the following correction
+factor table for the errata:
+
++---------------+---------------+---------------+-----------------+
+|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.
--
2.28.0
\
 
 \ /
  Last update: 2020-10-14 02:51    [W:0.078 / U:1.964 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site