Please note that this proposal is from this engineer and not from the company
he works for.
This SHOULD also fulfills any legal notification of work done, but not
submitted to the Linux Kernel.
Transfer of Information : Notification & Proposal of Feasibility to Support
System V Release 4 Defacto Standard Scheduling Extensions, etc within Linux
——————————-
SCHED_IA
Over 10 years ago, System V Release 4 was enhanced with additional
features by Sun Microsystems. One of the more minor extensions dealt with the
subdivision of process’s scheduling characteristics and was known as he
INTERACTIVE /IA scheduling class. This scheduling class was targeted to
frequent sleepers, with the mouse icon being one the first processes/tasks..
Linux has no explicit SCHED_IA scheduling policy, but does alter
scheduling characteristics based on some sleep behavior (example:
GENTLE_FAIR_SLEEPERS) within the fair share scheduling configuration option.
Processes / tasks that are CPU bound that fit into a SLEEPER behavior can have
a hybrid behavior over time where during any one scheduling period, it may
consume its variable length allocated time. This can alter its expected short
latency to be current / ONPROC. To simplify the implementation, it is suggested
that SCHED_IA be a sub scheduling policy of SCHED_NORMAL. Shouldn’t an
administrator be able to classify that the NORMAL long term behavior of a task,
be one as a FIXED sleeper?
Thus, the first Proposal is to explicitly support the SCHED_IA
scheduling policy within the Linux kernel. After kernel support, any
application that has the same functionality as priocntl(1) then needs to be
altered to support this new scheduling policy.
Note: Administrator in this context should be a task with a UID, EUID, GID,
EGID, etc, that has the proper CAPABILITY to alter scheduling behavior.
SCHED_UNFAIR
UNIX / Linux scheduling has in the most part attempts to
achieve some level of process / task scheduling fairness within the Linux
scheduler using the fair share scheduling class. Exceptions do exist, but are
not being discussed below. In general this type of scheduling is acceptable in
a generic implementation, but has weaknesses when UNIX / Linux is moved into a
different environment. Many companies use UNIX / Linux in heavy networking
environments where one or more tasks can infrequently attempt to consume more
than its fair share in a window scheduling period.
This proposal is to acknowledge that “nice” and a few other
scheduling workarounds do no always suffice to allow this temporary inequality
to exist. Yes, a cpumask could be set that allows only certain tasks to run on
specific nodes, however the implied assumption is that they only infrequently
need to have inequality / greater “time slice” than their fair share. A network
protocol task example is a convergence task that needs to run until it is
finished and until that happens needed routing changes will not occur. The time
window in which all tasks need to be run, SHOULD not need this task in
consecutive time windows, thus over longer periods of time, it still fulfills
the fair scheduling policy. Again the proper CAPABILITY needs to be specified
with the priocntl(1) like application as running many tasks per CPU COULD then
effect the performance of the system.
Thus, explicit support for a new SCHED_UNFAIR scheduling policy
is proposed / suggested within the Linux kernel. Again it can be a sub
scheduling policy of SCHED_NORMAL.
If there is an expressed need / want for this type of
functionality to be patched into a git, please inform this engineer if any
additional information is to be provided since this minimal TOI document is
more architecture / enhancement based and does not deal into any details as to
a possible implementation of the above additional functionality.
Thank you,
Mitchell Erblich
UNIX Kernel Engineer--
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