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b133207deb
Add the deadline monitors collection to validate the deadline scheduler,
both for deadline tasks and servers.
The currently implemented monitors are:
* nomiss:
validate dl entities run to completion before their deadiline
Reviewed-by: Nam Cao <namcao@linutronix.de>
Reviewed-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lore.kernel.org/r/20260330111010.153663-13-gmonaco@redhat.com
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
85 lines
5.0 KiB
ReStructuredText
85 lines
5.0 KiB
ReStructuredText
Deadline monitors
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=================
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- Name: deadline
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- Type: container for multiple monitors
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- Author: Gabriele Monaco <gmonaco@redhat.com>
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Description
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-----------
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The deadline monitor is a set of specifications to describe the deadline
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scheduler behaviour. It includes monitors per scheduling entity (deadline tasks
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and servers) that work independently to verify different specifications the
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deadline scheduler should follow.
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Specifications
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--------------
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Monitor nomiss
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~~~~~~~~~~~~~~
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The nomiss monitor ensures dl entities get to run *and* run to completion
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before their deadline, although deferrable servers may not run. An entity is
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considered done if ``throttled``, either because it yielded or used up its
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runtime, or when it voluntarily starts ``sleeping``.
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The monitor includes a user configurable deadline threshold. If the total
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utilisation of deadline tasks is larger than 1, they are only guaranteed
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bounded tardiness. See Documentation/scheduler/sched-deadline.rst for more
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details. The threshold (module parameter ``nomiss.deadline_thresh``) can be
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configured to avoid the monitor to fail based on the acceptable tardiness in
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the system. Since ``dl_throttle`` is a valid outcome for the entity to be done,
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the minimum tardiness needs be 1 tick to consider the throttle delay, unless
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the ``HRTICK_DL`` scheduler feature is active.
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Servers have also an intermediate ``idle`` state, occurring as soon as no
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runnable task is available from ready or running where no timing constraint
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is applied. A server goes to sleep by stopping, there is no wakeup equivalent
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as the order of a server starting and replenishing is not defined, hence a
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server can run from sleeping without being ready::
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sched_wakeup v
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dl_replenish;reset(clk) -- #=========================#
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| H H dl_replenish;reset(clk)
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+-----------> H H <--------------------+
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H H |
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+- dl_server_stop ---- H ready H |
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| +-----------------> H clk < DEADLINE_NS() H dl_throttle; |
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| | H H is_defer == 1 |
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| | sched_switch_in - H H -----------------+ |
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| | | #=========================# | |
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| | | | ^ | |
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| | | dl_server_idle dl_replenish;reset(clk) | |
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| | | v | | |
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| | | +--------------+ | |
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| | | +------ | | | |
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| | | dl_server_idle | | dl_throttle | |
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| | | | | idle | -----------------+ | |
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| | | +-----> | | | | |
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| | | | | | | |
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| | | | | | | |
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+--+--+---+--- dl_server_stop -- +--------------+ | | |
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| | | | | ^ | | |
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| | | | sched_switch_in dl_server_idle | | |
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| | | | v | | | |
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| | | | +---------- +---------------------+ | | |
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| | | | sched_switch_in | | | | |
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| | | | sched_wakeup | | | | |
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| | | | dl_replenish; | running | -------+ | | |
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| | | | reset(clk) | clk < DEADLINE_NS() | | | | |
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| | | | +---------> | | dl_throttle | | |
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| | | +----------------> | | | | | |
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| | | +---------------------+ | | | |
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| | sched_wakeup ^ sched_switch_suspend | | | |
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v v dl_replenish;reset(clk) | dl_server_stop | | | |
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+--------------+ | | v v v |
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| | - sched_switch_in + | +---------------+
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| | <---------------------+ dl_throttle +-- | |
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| sleeping | sched_wakeup | | throttled |
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| | -- dl_server_stop dl_server_idle +-> | |
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| | dl_server_idle sched_switch_suspend +---------------+
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+--------------+ <---------+ ^
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+------ dl_throttle;is_constr_dl == 1 || is_defer == 1 ------+
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