In preparation of upstreaming, let's set the min version requirement at the
released v6.9 kernels. Drop support for missing sched_ext_ops.exit_dump_len.
The open helper macros now check the existence of the field and abort if
missing.
In preparation of upstreaming, let's set the min version requirement at the
released v6.9 kernels. Drop support for missing sched_ext_ops.hotplug_seq.
The open helper macros now check the existence of the field and abort if
missing.
In preparation of upstreaming, let's set the min version requirement at the
released v6.9 kernels. Drop __COMPAT_scx_bpf_cpuperf_*(). The open helper
macros now check the existence of scx_bpf_cpuperf_cap() and abort if not.
In preparation of upstreaming, let's set the min version requirement at the
released v6.9 kernels. Drop __COMPAT_HAS_CPUMASKS(). The open helper macros
now check the existence of scx_bpf_nr_cpu_ids() and abort if not.
In preparation of upstreaming, let's set the min version requirement at the
released v6.9 kernels. Drop __COMPAT_scx_bpf_dump(). The open helper macros
now check the existence of scx_bpf_dump_bstr() and abort if not.
While at it, reorder the min requirement checks so that newly added ones are
up top to make testing easier.
In preparation of upstreaming, let's set the min version requirement at the
released v6.9 kernels. Drop __COMPAT_scx_bpf_exit(). The open helper macros
now check the existence of scx_bpf_exit_bstr() and abort if not.
In preparation of upstreaming, let's set the min version requirement at the
released v6.9 kernels. Drop __COMPAT_SCX_KICK_IDLE. The open helper macros
now check the existence of SCX_KICK_IDLE and abort if not.
There's no guarantee that errno is set or contains relevant information when
SCX_BUG() is invoked. This sometimes leads to "task failed successfully"
messages:
# ./scx_simple
../scheds/c/scx_simple.c:72 [scx panic]: Success
SCX_OPS_SWITCH_PARTIAL missing, kernel too old?
While not critical, it's not great. Let's update it so that errno is printed
in parentheses when non-zero and match the tag to the macro name so that
what's printed is the following:
# ./scx_simple
[SCX_BUG] ../scheds/c/scx_simple.c:72
SCX_OPS_SWITCH_PARTIAL missing, kernel too old?
In preparation of upstreaming, let's set the min version requirement at the
released v6.9 kernels. Drop __COMPAT_scx_bpf_switch_call(). The open helper
macros now check the existence of SCX_OPS_SWITCH_PARTIAL and abort if not.
scx_ops_open!() and scx_ops_attach!() could return the calling function
after an error, which can be surprising. Forutnately, as all the current
callers are either unwrapping or returning on error, the surprising behavior
is currently not very noticeable.
Fix it by breaking out of the macro block on errors.
With commit 786ec0c0 ("scx_rlfifo: schedule all tasks in user-space")
all the scheduling decisions are now happening in user-space. This also
bypasses the built-in idle selection logic, delegating the CPU selection
for each task to the user-space scheduler.
The easiest way to distribute tasks across the available CPUs is to
simply allow to dispatch them on the first CPU available.
In this way the scheduler becomes usable in practical scenarios and at
the same time it also maintains its simplicity.
This allows to spread all tasks across all the available CPUs
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Disable all the BPF optimization shortcuts by default and force all
tasks to be processed by the user-space scheduler.
Given that the primary goal of this scheduler is to offer a
straightforward and intuitive example for experimental purposes, this
change simplifies the process for individuals looking to experiment,
allowing them to apply changes to user-space code and quickly observe
the effects, without dealing with any in-kernel optimizations.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
No functional change, just add some comments to better describe the
parameters used when initializing the main BpfScheduler object.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
The bpf_ prefix is used for BPF API. Rename bpf_log2() to u32_log2() and
bpf_log2l() to u64_log2(). While at it, relocate them below compiler
directive helpers.
The same change was previously applied with commit 8820af8d
("scx_rustland: enable user-space scheduler to preempt other tasks").
However, it was reverted in commit 732ba490 ("scx_rustland: avoid using
SCX_ENQ_PREEMPT") with the introduction of the global dynamic time
slice (inversely proportional to the number of running tasks), because
it already provided sufficient context switch opportunities, negating
any advantage of the preemption.
With the introduction of the virtual time slice in commit 6f4cd853
("scx_rustland: introduce virtual time slice"), re-introducing the
ability for the user-space scheduler to preempt other tasks now appears
beneficial again.
As confirmed by experimental results, this change helps prevent
potential audio cracking issues and enhances overall system
responsiveness, resulting in a 4-5% increase in fps performing the
usual benchmark of gaming while recompiling the kernel.
Tested-by: SoulHarsh007 <harsh.peshwani@outlook.com>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Tasks dispatched directly using SCX_DSQ_LOCAL may receive excessively
high priority compared to those dispatched by the user-space scheduler.
To avoid this priority disparity, dispatch tasks to the per-CPU DSQs
using direct dispatch and reserve SCX_DSQ_LOCAL for per-CPU kthreads
only.
Tested-by: Tested-by: SoulHarsh007 <harsh.peshwani@outlook.com>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Keep track of the maximum vruntime among all tasks and flush them if the
difference between the maximum and minimum vruntime exceeds slice_ns.
This helps to prevent excessive starvation, as every task is guaranteed
to be dispatched within the slice_ns time limit.
Tested-by: Tested-by: SoulHarsh007 <harsh.peshwani@outlook.com>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Add a small section to document how to use SCX_SCHEDULER_OVERRIDE and
SCX_FLAGS_OVERRIDE with the scx systemd service.
Also fix a small typo (namspace -> namespace).
Signed-off-by: Pietro Righi <pietro.righi.email@gmail.com>
Switching the scheduler requires changing SCX_SCHEDULER (and potentially
also SCX_FLAGS) in /etc/default/scx.
This patch allows overriding these settings using systemd environment
variables SCX_SCHEDULER_OVERRIDE and SCX_FLAGS_OVERRIDE, without
changing the default configuration.
Example:
> grep SCX_SCHEDULER /etc/default/scx
SCX_SCHEDULER=scx_rusty
> sudo systemctl status scx
...
Main PID: 8021 (scx_rusty)
...
> sudo systemctl set-environment SCX_SCHEDULER_OVERRIDE=scx_rustland
> sudo systemctl restart scx
> sudo systemctl status scx
...
Main PID: 4021 (scx_rustland)
...
This feature can be useful for quickly testing different schedulers and
settings, without altering the global system configuration.
Signed-off-by: Pietro Righi <pietro.righi.email@gmail.com>
These are used in mitosis, but they belong in common code so other
schedulers can do css iteration.
Signed-off-by: Dan Schatzberg <schatzberg.dan@gmail.com>
If LLVM is compiled with the LLVM_VERSION_SUFFIX cmake option, then the
version may have an additional suffix, for example "18.1.7+libcxx".
Gentoo for example uses this to fend off ABI issues between libstdc++
and libc++.
Signed-off-by: Violet Purcell <vimproved@inventati.org>
The old logic for CPU frequency scaling is that the task's CPU
performance target (i.e., target CPU frequency) is checked every tick
interval and updated immediately. Indeed, it samples and updates a
performance target every tick interval. Ultimately, it fluctuates CPU
frequency every tick interval, resulting in less steady performance.
Now, we take a different strategy. The key idea is to increase the
frequency as soon as possible when a task starts running for quick
adoption to load spikes. However, if necessary, it decreases gradually
every tick interval to avoid frequency fluctuations.
In my testing, it shows more stable performance in many workloads
(games, compilation).
Signed-off-by: Changwoo Min <changwoo@igalia.com>
Originally, do_update_sys_stat() simply calculated the system-wide CPU
utilization. Over time, it has evolved to collect all kinds of
system-wide, periodic statistics for decision-making, so it has become
bulky. Now, it is time to refactor it for readability. This commit does
not contain functional changes other than refactoring.
Signed-off-by: Changwoo Min <changwoo@igalia.com>
The periodic CPU utilization routine does a lot of other work now. So we
rename LAVD_CPU_UTIL_INTERVAL_NS to LAVD_SYS_STAT_INTERVAL_NS.
Signed-off-by: Changwoo Min <changwoo@igalia.com>
When a device is suspended and resumed, the suspended duration is added
up to a task's runtime if the task was running on the CPU. After the
resume, the task's runtime is incorrectly long and the scheduler starts
to recognize the system is under heavy load. To avoid such problem, the
suspended duration is measured and substracted from the task's runtime.
Signed-off-by: Changwoo Min <changwoo@igalia.com>
scx_mitosis is a dynamic affinity scheduler which assigns cgroups to
Cells and Cells to discrete sets of CPUs. The number of cells is dynamic
as is the CPU assignment. BPF mostly just does vtime scheduling for each
cell, tracks load, and responds to reconfiguration from userspace.
Userspace makes decisions about how to assign cgroups to cells and cells
to cpus.
This is not yet a complete scheduler, much of the userspace logic is a
placeholder as I experiment with better logic. I also want to add richer
scheduling semantics to userspace, e.g. so that cells can do more
"soft-affinity" rather than the strict partitioning implemented
currently.
Signed-off-by: Dan Schatzberg <schatzberg.dan@gmail.com>
