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 <b...@alien8.de> Signed-off-by: Fenghua Yu <fenghua...@intel.com> Reviewed-by: Tony Luck <tony.l...@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
