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The current SCHED_DEADLINE (DL) admission control ensures that
sum of reserved CPU bandwidth < x * M
where
x = /proc/sys/kernel/sched_rt_{runtime,period}_us
M = # CPUs in root domain.
DL admission control works well for homogeneous systems where the
capacity of all CPUs are equal (1024). I.e. bounded tardiness for DL
and non-starvation of non-DL tasks is guaranteed.
But on heterogeneous systems where capacity of CPUs are different it
could fail by over-allocating CPU time on smaller capacity CPUs.
On an Arm big.LITTLE/DynamIQ system DL tasks can easily starve other
tasks making it unusable.
Fix this by explicitly considering the CPU capacity in the DL admission
test by replacing M with the root domain CPU capacity sum.
Signed-off-by: Luca Abeni <luca.abeni@santannapisa.it>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lkml.kernel.org/r/20200520134243.19352-4-dietmar.eggemann@arm.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.