From d1b22e36e3188f47dbf8aaef54d9e79df8e91f4c Mon Sep 17 00:00:00 2001 From: Fenghua Yu Date: Wed, 14 Oct 2020 00:49:26 +0000 Subject: [PATCH] Documentation/x86: Rename resctrl_ui.rst and add two errata to the file 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 Signed-off-by: Fenghua Yu Signed-off-by: Borislav Petkov Reviewed-by: Tony Luck Link: https://lkml.kernel.org/r/20201014004927.1839452-2-fenghua.yu@intel.com --- Documentation/x86/index.rst | 2 +- .../x86/{resctrl_ui.rst => resctrl.rst} | 93 +++++++++++++++++++ 2 files changed, 94 insertions(+), 1 deletion(-) rename Documentation/x86/{resctrl_ui.rst => resctrl.rst} (90%) diff --git a/Documentation/x86/index.rst b/Documentation/x86/index.rst index b224d12c880bc..9c6ebf355f81d 100644 --- a/Documentation/x86/index.rst +++ b/Documentation/x86/index.rst @@ -27,7 +27,7 @@ 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 90% rename from Documentation/x86/resctrl_ui.rst rename to Documentation/x86/resctrl.rst index e59b7b93a9b49..71a531061e4e2 100644 --- a/Documentation/x86/resctrl_ui.rst +++ b/Documentation/x86/resctrl.rst @@ -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. -- 2.30.2