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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
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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
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These are all obvious typos.
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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"If the MBA is specified in MB then user can enter the max b/w in MB"
is a tautology. How can the user know if the schemata takes a percentage
or a MB/s value?
This is referring to whether the software controller is interpreting
the schemata's value. Make this clear.
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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"L2 cache does not support code and data prioritization". This isn't
true, elsewhere the document says it can be enabled with the cdpl2
mount option.
While we're here, these sample strings have lower-case code/data,
which isn't how the kernel exports them.
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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Since commit 4d05bf71f157 ("x86/resctrl: Introduce AMD QOS feature")
resctrl has supported non-contiguous cache bit masks. The interface
for this is currently try-it-and-see.
Update the documentation to say Intel CPUs have this requirement,
instead of X86.
Cc: Babu Moger <Babu.Moger@amd.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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This converts the plain text documentation to reStructuredText format and
add it to Sphinx TOC tree. No essential content change.
Signed-off-by: Changbin Du <changbin.du@gmail.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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