Refactor the main module for scx_layered to move metrics into a separate
module. This change does no functional differences, only code structure.
This will make it a little easier to navigate the logic in the main
scheduler code.
Signed-off-by: Daniel Hodges <hodges.daniel.scott@gmail.com>
That is okay since the runtime is considered in calculating a virtual
deadline. A shorter runtime will result in a tighter deadline linearly.
Signed-off-by: Changwoo Min <changwoo@igalia.com>
If inheriting the parent's properties, a new fork task tends to be too
prioritized. That is, many parent processes, such as `make,` are a bit
more latency-critical than average.
Signed-off-by: Changwoo Min <changwoo@igalia.com>
Instead of using a static value to classify tasks based on their average
amount of voluntary context switches, try to periodically evaluate an
optimal threshold, based on a global average of voluntary context
switches among of all the running tasks.
Tasks with an average amount of voluntary context switches greater than
the global average will be classified as interactive.
The global average is evaluated as an exponentially weighted moving
average (EWMA), as:
avg(t) = avg(t - 1) * 0.75 - task_avg(t) * 0.25
This approach is more efficient than iterating through all tasks and it
helps to prevent rapid fluctuations that may be caused by bursts of
voluntary context switch events.
The dynamic nvcsw threshold enables a more precise adjustment of
the classification criteria to swiftly respond to global system changes:
tasks can be quickly classified as interactive, but if the system
experiences too many interactive events, the criteria for maintaining
interactive status become stricter. This creates a natural selection
process where only the most deserving tasks remain interactive.
Additionally, introduce the new option `--nvcsw-max-thresh N`, which
allows to extend or restrict the fluctuation range of the global average
threshold for voluntary context switches.
Tested-by: Piotr Gorski <piotrgorski@cachyos.org>
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>
Advancing the clock slower when overloaded gives more opportunities for
latency-critical tasks to cut in the run queue. Controlling the clock
better reflects the actual load than the prior approach of stretching
the time-space when overloaded.
Signed-off-by: Changwoo Min <changwoo@igalia.com>
We now maintain two run queues—an eligible run queue (DSQ) and an
ineligible run queue (rbtree)—sorted by the task's virtual deadline.
When the eligible run queue is empty, or the ineligible run queue has
not been consumed for too long (e.g., 15 msec), a task in the ineligible
run queue is moved to the eligible run queue for execution. With these
two queues, we have a better admission control.
Signed-off-by: Changwoo Min <changwoo@igalia.com>
Followed commit 1c3b563, move the checking of task.migrated.get() into
the vector filter. In this way, we can remove the skip_while() call in
find_first_candidate().
Signed-off-by: I Hsin Cheng <richard120310@gmail.com>
Update libbpf-rs & libbpf-cargo to 0.24. Among other things, generated
skeletons now contain directly accessible map and program objects, no
longer necessitating the use of accessor methods. As a result, the risk
for mutability conflicts is reduced greatly.
Signed-off-by: Daniel Müller <deso@posteo.net>
This change refactors some of the helper methods for getting the
preferred node for tasks using mempolicy. The load balancing logic in
try_find_move_task is updated to allow for a filter, which is used to
filter for tasks with a preferred mempolicy.
Signed-off-by: Daniel Hodges <hodges.daniel.scott@gmail.com>
This change makes scx_rusty mempolicy aware. When a process uses
set_mempolicy it can change NUMA memory preferences and cause
performance issues when tasks are scheduled on remote NUMA nodes. This
change modifies task_pick_domain to use the new helper method that
returns the preferred node id.
Signed-off-by: Daniel Hodges <hodges.daniel.scott@gmail.com>
Estimating the service time from run time and frequency is not
incorrect. However, it reacts slowly to sudden changes since it relies
on the moving average. Hence, we directly measure the service time to
enforce fairness.
Signed-off-by: Changwoo Min <changwoo@igalia.com>
Add the LLC id to the Cpu struct, which will make it easier for
referencing the LLC when doing operations on a Cpu.
Signed-off-by: Daniel Hodges <hodges.daniel.scott@gmail.com>
Instead of performing domain mask checking inside
"find_first_candidate()" every time, check whether the tasks within push
domain are abled to run on pull domain by performing the mask check at
vector generation stage.
This way can also avoid repeated computation generated by the same
(task, pull_dom) pair as they'll try to check whether the pull domain is
in the task domain mask.
Also since whether a task is a kworker won't change in time, we can
perform the check earlier and put it in the filter, too.
Signed-off-by: I Hsin Cheng <richard120310@gmail.com>
We always use nr_cpu_ids to represent the maximum CPU id returned by
scx_bpf_nr_cpu_ids().
Replace cpu_max with nr_cpu_ids to be more consistent with the rest of
the code.
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>
The kernel from kernel.org lacks the necessary .config chunk required
by the build via virtme-ng.
To fix this, include the kernel .config chunk directly in the scx
repository and use it from here.
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>
We can rely on scx_bpf_nr_cpu_ids() to create all the possible per-CPU
DSQs, eliminating the need for the hard-coded limit MAX_CPUS.
In this way scx_bpfland can support the same amount of CPUs that the
kernel can handle.
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>
Instead of constantly checking the need to drain tasks from the DSQs of
the offline CPUs, provide an atomic flag to notify when there are tasks
to be drained from the offline CPUs.
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>
Refine the safeguard mechanism to avoid generating too many interactive
tasks in the system, which could nullify the effect of the
interactive/regular task classification.
The safeguard mechanism operates by pausing the promotion of new tasks
to interactive status during the task wake-up process, whenever the
number of interactive tasks in the priority queue exceeds a specific
limit (set to 4x the number of online CPUs).
Halting the promotion of additional interactive tasks allows to
prioritize those already classified as interactive, thereby preventing
potential "bursts" of excessive interactive tasks in the system.
This refines the mitigation already provided by commit 640bd562
("scx_bpfland: prevent tasks from abusing interactive priority boost").
Fixes: 640bd562 ("scx_bpfland: prevent tasks from abusing interactive priority boost")
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>
Always assign the maximum time slice if there are idle CPUs in the
system.
Otherwise, double the task's unused time slice to reward tasks that use
less CPU time and at the same time refill the time slice of the tasks
every time they're dispatched.
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>
