Dear developers,
starting from release 3.14, every Linux kernel has an additional CPU
scheduling policy called *SCHED_DEADLINE* [1, 2].
This email is to encourage you in evaluating the benefits that such a
policy could bring when scheduling the Android services.
The policy allows to assign each task two timing information: a runtime Qi
and a period Pi.
The Linux kernel will then schedule the task so that it receives the CPU
exactly for a time equal to Qi every period Pi (the task will therefore get
a CPU share exactly equal to Qi/Pi).
References [1] and [2] provide further information about the specific
algorithm.
The interesting thing about this policy is the so called *temporal
isolation*: the timing execution of a task is not be affected by the
behaviour of the other tasks running on the system.
This way, if a task misbehaves trying to use a resource for a time longer
than expected, it is stopped and cannot affect the timing performance of
the other tasks running in the system.
This property can be leveraged for two goals:
- Providing timing guarantees to time-sensitive Android services: if
scheduled with SCHED_DEADLINE, the Android service will be guaranteed to
receive the specified share of CPU time, regardless of the behaviour of the
other tasks running on the system.
- Enforcing timing confinement of (untrusted) Android services: the
service will be forced to use no more than its assigned CPU share.
This is useful to limit the amount of CPU used by high-priority services
which, in case of bug or intensive computation, may starve the rest of the
system.
An interesting experimental comparison of SCHED_DEADLINE vs SCHED_FIFO and
SCHED_OTHER is available at [3] (unfortunately, it's not free).
Best regards,
Claudio
[1] SCHED_DEADLINE on Wikipedia:
https://en.wikipedia.org/wiki/SCHED_DEADLINE
[2] Documentation in the Linux kernel:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/scheduler/sched-deadline.txt
[3] Deadline scheduling in the Linux kernel,
http://onlinelibrary.wiley.com/doi/10.1002/spe.2335/abstract
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