In sched_ext API, a repeatedly reported pain point is the overuse of the
verb "dispatch" and confusion around "consume":
- ops.dispatch()
- scx_bpf_dispatch[_vtime]()
- scx_bpf_consume()
- scx_bpf_dispatch[_vtime]_from_dsq*()
This overloading of the term is historical. Originally, there were only
built-in DSQs and moving a task into a DSQ always dispatched it for
execution. Using the verb "dispatch" for the kfuncs to move tasks into these
DSQs made sense.
Later, user DSQs were added and scx_bpf_dispatch[_vtime]() updated to be
able to insert tasks into any DSQ. The only allowed DSQ to DSQ transfer was
from a non-local DSQ to a local DSQ and this operation was named "consume".
This was already confusing as a task could be dispatched to a user DSQ from
ops.enqueue() and then the DSQ would have to be consumed in ops.dispatch().
Later addition of scx_bpf_dispatch_from_dsq*() made the confusion even worse
as "dispatch" in this context meant moving a task to an arbitrary DSQ from a
user DSQ.
Clean up the API with the following renames:
1. scx_bpf_dispatch[_vtime]() -> scx_bpf_dsq_insert[_vtime]()
2. scx_bpf_consume() -> scx_bpf_dsq_move_to_local()
3. scx_bpf_dispatch[_vtime]_from_dsq*() -> scx_bpf_dsq_move[_vtime]*()
This patch performs the first set of renames. Compatibility is maintained
by:
- The previous kfunc names are still provided by the kernel so that old
binaries can run. Kernel generates a warning when the old names are used.
- compat.bpf.h provides wrappers for the new names which automatically fall
back to the old names when running on older kernels. They also trigger
build error if old names are used for new builds.
The compat features will be dropped after v6.15.
v2: Documentation updates.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Andrea Righi <arighi@nvidia.com>
Acked-by: Changwoo Min <changwoo@igalia.com>
Acked-by: Johannes Bechberger <me@mostlynerdless.de>
Acked-by: Giovanni Gherdovich <ggherdovich@suse.com>
Cc: Dan Schatzberg <dschatzberg@meta.com>
Cc: Ming Yang <yougmark94@gmail.com>
4c30f5ce4f ("sched_ext: Implement scx_bpf_dispatch[_vtime]_from_dsq()")
added four kfuncs for dispatching while iterating. They are allowed from the
dispatch and unlocked contexts but two of the kfuncs were only added in the
dispatch section. Add missing declarations in the unlocked section.
Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 4c30f5ce4f ("sched_ext: Implement scx_bpf_dispatch[_vtime]_from_dsq()")
Update the comments in sched_ext_ops to clarify this table is for
a BPF scheduler and a userland scheduler should also rely on the
sched_ext_ops table through the BPF scheduler.
Signed-off-by: Changwoo Min <changwoo@igalia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
On 2 x Intel Sapphire Rapids machines with 224 logical CPUs, a poorly
behaving BPF scheduler can live-lock the system by making multiple CPUs bang
on the same DSQ to the point where soft-lockup detection triggers before
SCX's own watchdog can take action. It also seems possible that the machine
can be live-locked enough to prevent scx_ops_helper, which is an RT task,
from running in a timely manner.
Implement scx_softlockup() which is called when three quarters of
soft-lockup threshold has passed. The function immediately enables the ops
breather and triggers an ops error to initiate ejection of the BPF
scheduler.
The previous and this patch combined enable the kernel to reliably recover
the system from live-lock conditions that can be triggered by a poorly
behaving BPF scheduler on Intel dual socket systems.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Douglas Anderson <dianders@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
A poorly behaving BPF scheduler can live-lock the system by e.g. incessantly
banging on the same DSQ on a large NUMA system to the point where switching
to the bypass mode can take a long time. Turning on the bypass mode requires
dequeueing and re-enqueueing currently runnable tasks, if the DSQs that they
are on are live-locked, this can take tens of seconds cascading into other
failures. This was observed on 2 x Intel Sapphire Rapids machines with 224
logical CPUs.
Inject artifical delays while the bypass mode is switching to guarantee
timely completion.
While at it, move __scx_ops_bypass_lock into scx_ops_bypass() and rename it
to bypass_lock.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Valentin Andrei <vandrei@meta.com>
Reported-by: Patrick Lu <patlu@meta.com>
Pull sched_ext/for-6.12-fixes to receive 0e7ffff1b8 ("scx: Fix raciness in
scx_ops_bypass()"). Planned updates for scx_ops_bypass() depends on it.
Signed-off-by: Tejun Heo <tj@kernel.org>
There is no reason to use a bitwise AND when checking the conditions to
enable NUMA optimization for the built-in CPU idle selection policy, so
use a logical AND instead.
Fixes: f6ce6b9493 ("sched_ext: Do not enable LLC/NUMA optimizations when domains overlap")
Reported-by: Nathan Chancellor <nathan@kernel.org>
Closes: https://lore.kernel.org/lkml/20241108181753.GA2681424@thelio-3990X/
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
When the LLC and NUMA domains fully overlap, enabling both optimizations
in the built-in idle CPU selection policy is redundant, as it leads to
searching for an idle CPU within the same domain twice.
Likewise, if all online CPUs are within a single LLC domain, LLC
optimization is unnecessary.
Therefore, detect overlapping domains and enable topology optimizations
only when necessary.
Moreover, rely on the online CPUs for this detection logic, instead of
using the possible CPUs.
Fixes: 860a45219b ("sched_ext: Introduce NUMA awareness to the default idle selection policy")
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Similarly to commit dfa4ed29b1 ("sched_ext: Introduce LLC awareness to
the default idle selection policy"), extend the built-in idle CPU
selection policy to also prioritize CPUs within the same NUMA node.
With this change applied, the built-in CPU idle selection policy follows
this logic:
- always prioritize CPUs from fully idle SMT cores,
- select the same CPU if possible,
- select a CPU within the same LLC domain,
- select a CPU within the same NUMA node.
Both NUMA and LLC awareness features are enabled only when the system
has multiple NUMA nodes or multiple LLC domains.
In the future, we may want to improve the NUMA node selection to account
the node distance from prev_cpu. Currently, the logic only tries to keep
tasks running on the same NUMA node. If all CPUs within a node are busy,
the next NUMA node is chosen randomly.
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
ops.dispatch() and ops.yield() may be fed a NULL task_struct pointer.
set_arg_maybe_null() is used to tell the verifier that they should be NULL
checked before being dereferenced. BPF now has an a lot prettier way to
express this - tagging arguments in CFI stubs with __nullable. Replace
set_arg_maybe_null() with __nullable CFI stub tags.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>
Acked-by: Martin KaFai Lau <martin.lau@kernel.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>
CFI stubs can be used to tag arguments with __nullable (and possibly other
tags in the future) but for that to work the CFI stubs must have names that
are recognized by BPF. Rename them.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>
Acked-by: Martin KaFai Lau <martin.lau@kernel.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Rely on the scheduler topology information to implement basic LLC
awareness in the sched_ext build-in idle selection policy.
This allows schedulers using the built-in policy to make more informed
decisions when selecting an idle CPU in systems with multiple LLCs, such
as NUMA systems or chiplet-based architectures, and it helps keep tasks
within the same LLC domain, thereby improving cache locality.
For efficiency, LLC awareness is applied only to tasks that can run on
all the CPUs in the system for now. If a task's affinity is modified
from user space, it's the responsibility of user space to choose the
appropriate optimized scheduling domain.
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Update ops.select_cpu() documentation to clarify that this method is not
called for tasks that are restricted to run on a single CPU, as these
tasks do not have the option to select a different CPU.
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
In the sched_ext built-in idle CPU selection logic, when handling a
WF_SYNC wakeup, we always attempt to migrate the task to the waker's
CPU, as the waker is expected to yield the CPU after waking the task.
However, it may be preferable to keep the task on its previous CPU if
the waker's CPU is cache-affine.
The same approach is also used by the fair class and in other scx
schedulers, like scx_rusty and scx_bpfland.
Therefore, apply the same logic to the built-in idle CPU selection
policy as well.
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
Signed-off-by: Tejun Heo <tj@kernel.org>
As described in commit b07996c7ab ("sched_ext: Don't hold
scx_tasks_lock for too long"), we're doing a cond_resched() every 32
calls to scx_task_iter_next() to avoid RCU and other stalls. That commit
also added a cpu_relax() to the codepath where we drop and reacquire the
lock, but as Waiman described in [0], cpu_relax() should only be
necessary in busy loops to avoid pounding on a cacheline (or to allow a
hypertwin to more fully utilize a core).
Let's remove the unnecessary cpu_relax().
[0]: https://lore.kernel.org/all/35b3889b-904a-4d26-981f-c8aa1557a7c7@redhat.com/
Cc: Waiman Long <llong@redhat.com>
Signed-off-by: David Vernet <void@manifault.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Iterating with scx_task_iter involves scx_tasks_lock and optionally the rq
lock of the task being iterated. Both locks can be released during iteration
and the iteration can be continued after re-grabbing scx_tasks_lock.
Currently, all lock handling is pushed to the caller which is a bit
cumbersome and makes it difficult to add lock-aware behaviors. Make the
scx_task_iter helpers handle scx_tasks_lock.
- scx_task_iter_init/scx_taks_iter_exit() now grabs and releases
scx_task_lock, respectively. Renamed to
scx_task_iter_start/scx_task_iter_stop() to more clearly indicate that
there are non-trivial side-effects.
- Add __ prefix to scx_task_iter_rq_unlock() to indicate that the function
is internal.
- Add scx_task_iter_unlock/relock(). The former drops both rq lock (if held)
and scx_tasks_lock and the latter re-locks only scx_tasks_lock.
This doesn't cause behavior changes and will be used to implement stall
avoidance.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>
Bypass mode was depending on ops.select_cpu() which can't be trusted as with
the rest of the BPF scheduler. Always enable and use scx_select_cpu_dfl() in
bypass mode.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>
Move the sanity check from the inner function scx_select_cpu_dfl() to the
exported kfunc scx_bpf_select_cpu_dfl(). This doesn't cause behavior
differences and will allow using scx_select_cpu_dfl() in bypass mode
regardless of scx_builtin_idle_enabled.
Signed-off-by: Tejun Heo <tj@kernel.org>
The disable path caps p->scx.slice to SCX_SLICE_DFL. As the field is already
being ignored at this stage during disable, the only effect this has is that
when the next BPF scheduler is loaded, it won't see unreasonable left-over
slices. Ultimately, this shouldn't matter but it's better to start in a
known state. Drop p->scx.slice capping from the disable path and instead
reset it to SCX_SLICE_DFL in the enable path.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>
This reverts commit 6f34d8d382.
Slice length is ignored while bypassing and tasks are switched on every tick
and thus the patch does not make any difference. The perceived difference
was from test noise.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>
pick_next_task_scx() was turned into pick_task_scx() since
commit 753e2836d1 ("sched_ext: Unify regular and core-sched pick
task paths"). Update the outdated message.
Signed-off-by: Honglei Wang <jameshongleiwang@126.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
scx_qmap and other schedulers in the SCX repo are using SCX_ENQ_WAKEUP to
tell whether ops.select_cpu() was called. This is incorrect as
ops.select_cpu() can be skipped in the wakeup path and leads to e.g.
incorrectly skipping direct dispatch for tasks that are bound to a single
CPU.
sched core has been updated to specify ENQUEUE_RQ_SELECTED if
->select_task_rq() was called. Map it to SCX_ENQ_CPU_SELECTED and update
scx_qmap to test it instead of SCX_ENQ_WAKEUP.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>
Cc: Daniel Hodges <hodges.daniel.scott@gmail.com>
Cc: Changwoo Min <multics69@gmail.com>
Cc: Andrea Righi <andrea.righi@linux.dev>
Cc: Dan Schatzberg <schatzberg.dan@gmail.com>
568894edbe ("sched_ext: Add scx_cgroup_enabled to gate cgroup operations
and fix scx_tg_online()") assumed that scx_cgroup_exit() is only called
after scx_cgroup_init() finished successfully. This isn't true.
scx_cgroup_exit() can be called without scx_cgroup_init() being called at
all or after scx_cgroup_init() failed in the middle.
As init state is tracked per cgroup, scx_cgroup_exit() can be used safely to
clean up in all cases. Remove the incorrect WARN_ON_ONCE().
Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 568894edbe ("sched_ext: Add scx_cgroup_enabled to gate cgroup operations and fix scx_tg_online()")
When the BPF scheduler fails, ops.exit() allows rich error reporting through
scx_exit_info. Use scx.exit() path consistently for all failures which can
be caused by the BPF scheduler:
- scx_ops_error() is called after ops.init() and ops.cgroup_init() failure
to record error information.
- ops.init_task() failure now uses scx_ops_error() instead of pr_err().
- The err_disable path updated to automatically trigger scx_ops_error() to
cover cases that the error message hasn't already been generated and
always return 0 indicating init success so that the error is reported
through ops.exit().
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: David Vernet <void@manifault.com>
Cc: Daniel Hodges <hodges.daniel.scott@gmail.com>
Cc: Changwoo Min <multics69@gmail.com>
Cc: Andrea Righi <andrea.righi@linux.dev>
Cc: Dan Schatzberg <schatzberg.dan@gmail.com>
The #endif trailing comment of CONFIG_EXT_GROUP_SCHED is unmatched, so fix
it.
Signed-off-by: Zhang Qiao <zhangqiao22@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
The enable path uses three big locks - scx_fork_rwsem, scx_cgroup_rwsem and
cpus_read_lock. Currently, the locks are grabbed together which is prone to
locking order problems.
For example, currently, there is a possible deadlock involving
scx_fork_rwsem and cpus_read_lock. cpus_read_lock has to nest inside
scx_fork_rwsem due to locking order existing in other subsystems. However,
there exists a dependency in the other direction during hotplug if hotplug
needs to fork a new task, which happens in some cases. This leads to the
following deadlock:
scx_ops_enable() hotplug
percpu_down_write(&cpu_hotplug_lock)
percpu_down_write(&scx_fork_rwsem)
block on cpu_hotplug_lock
kthread_create() waits for kthreadd
kthreadd blocks on scx_fork_rwsem
Note that this doesn't trigger lockdep because the hotplug side dependency
bounces through kthreadd.
With the preceding scx_cgroup_enabled change, this can be solved by
decoupling cpus_read_lock, which is needed for static_key manipulations,
from the other two locks.
- Move the first block of static_key manipulations outside of scx_fork_rwsem
and scx_cgroup_rwsem. This is now safe with the preceding
scx_cgroup_enabled change.
- Drop scx_cgroup_rwsem and scx_fork_rwsem between the two task iteration
blocks so that __scx_ops_enabled static_key enabling is outside the two
rwsems.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-and-tested-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
Link: http://lkml.kernel.org/r/8cd0ec0c4c7c1bc0119e61fbef0bee9d5e24022d.camel@linux.ibm.com
The disable path uses three big locks - scx_fork_rwsem, scx_cgroup_rwsem and
cpus_read_lock. Currently, the locks are grabbed together which is prone to
locking order problems. With the preceding scx_cgroup_enabled change, we can
decouple them:
- As cgroup disabling no longer requires modifying a static_key which
requires cpus_read_lock(), no need to grab cpus_read_lock() before
grabbing scx_cgroup_rwsem.
- cgroup can now be independently disabled before tasks are moved back to
the fair class.
Relocate scx_cgroup_exit() invocation before scx_fork_rwsem is grabbed, drop
now unnecessary cpus_read_lock() and move static_key operations out of
scx_fork_rwsem. This decouples all three locks in the disable path.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-and-tested-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
Link: http://lkml.kernel.org/r/8cd0ec0c4c7c1bc0119e61fbef0bee9d5e24022d.camel@linux.ibm.com
If the BPF scheduler does not implement ops.cgroup_init(), scx_tg_online()
didn't set SCX_TG_INITED which meant that ops.cgroup_exit(), even if
implemented, won't be called from scx_tg_offline(). This is because
SCX_HAS_OP(cgroupt_init) is used to test both whether SCX cgroup operations
are enabled and ops.cgroup_init() exists.
Fix it by introducing a separate bool scx_cgroup_enabled to gate cgroup
operations and use SCX_HAS_OP(cgroup_init) only to test whether
ops.cgroup_init() exists. Make all cgroup operations consistently use
scx_cgroup_enabled to test whether cgroup operations are enabled.
scx_cgroup_enabled is added instead of using scx_enabled() to ease planned
locking updates.
Signed-off-by: Tejun Heo <tj@kernel.org>
scx_ops_init_task() and the follow-up scx_ops_enable_task() in the fork path
were gated by scx_enabled() test and thus __scx_ops_enabled had to be turned
on before the first scx_ops_init_task() loop in scx_ops_enable(). However,
if an external entity causes sched_class switch before the loop is complete,
tasks which are not initialized could be switched to SCX.
The following can be reproduced by running a program which keeps toggling a
process between SCHED_OTHER and SCHED_EXT using sched_setscheduler(2).
sched_ext: Invalid task state transition 0 -> 3 for fish[1623]
WARNING: CPU: 1 PID: 1650 at kernel/sched/ext.c:3392 scx_ops_enable_task+0x1a1/0x200
...
Sched_ext: simple (enabling)
RIP: 0010:scx_ops_enable_task+0x1a1/0x200
...
switching_to_scx+0x13/0xa0
__sched_setscheduler+0x850/0xa50
do_sched_setscheduler+0x104/0x1c0
__x64_sys_sched_setscheduler+0x18/0x30
do_syscall_64+0x7b/0x140
entry_SYSCALL_64_after_hwframe+0x76/0x7e
Fix it by gating scx_ops_init_task() separately using
scx_ops_init_task_enabled. __scx_ops_enabled is now set after all tasks are
finished with scx_ops_init_task().
Signed-off-by: Tejun Heo <tj@kernel.org>
scx_ops_enable() has two task iteration loops. The first one calls
scx_ops_init_task() on every task and the latter switches the eligible ones
into SCX. The first loop left the tasks in SCX_TASK_INIT state and then the
second loop switched it into READY before switching the task into SCX.
The distinction between INIT and READY is only meaningful in the fork path
where it's used to tell whether the task finished forking so that we can
tell ops.exit_task() accordingly. Leaving task in INIT state between the two
loops is incosistent with the fork path and incorrect. The following can be
triggered by running a program which keeps toggling a task between
SCHED_OTHER and SCHED_SCX while enabling a task:
sched_ext: Invalid task state transition 1 -> 3 for fish[1526]
WARNING: CPU: 2 PID: 1615 at kernel/sched/ext.c:3393 scx_ops_enable_task+0x1a1/0x200
...
Sched_ext: qmap (enabling+all)
RIP: 0010:scx_ops_enable_task+0x1a1/0x200
...
switching_to_scx+0x13/0xa0
__sched_setscheduler+0x850/0xa50
do_sched_setscheduler+0x104/0x1c0
__x64_sys_sched_setscheduler+0x18/0x30
do_syscall_64+0x7b/0x140
entry_SYSCALL_64_after_hwframe+0x76/0x7e
Fix it by transitioning to READY in the first loop right after
scx_ops_init_task() succeeds.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: David Vernet <void@manifault.com>
scx_ops_enable() used preempt_disable() around the task iteration loop to
switch tasks into SCX to guarantee forward progress of the task which is
running scx_ops_enable(). However, in the gap between setting
__scx_ops_enabled and preeempt_disable(), an external entity can put tasks
including the enabling one into SCX prematurely, which can lead to
malfunctions including stalls.
The bypass mode can wrap the entire enabling operation and guarantee forward
progress no matter what the BPF scheduler does. Use the bypass mode instead
to guarantee forward progress while enabling.
While at it, release and regrab scx_tasks_lock between the two task
iteration locks in scx_ops_enable() for clarity as there is no reason to
keep holding the lock between them.
Signed-off-by: Tejun Heo <tj@kernel.org>
The distinction between SCX_OPS_PREPPING and SCX_OPS_ENABLING is not used
anywhere and only adds confusion. Drop SCX_OPS_PREPPING.
Signed-off-by: Tejun Heo <tj@kernel.org>
check_hotplug_seq() is used to detect CPU hotplug event which occurred while
the BPF scheduler is being loaded so that initialization can be retried if
CPU hotplug events take place before the CPU hotplug callbacks are online.
As such, the best place to call it is in the same cpu_read_lock() section
that enables the CPU hotplug ops. Currently, it is called in the next
cpus_read_lock() block in scx_ops_enable(). The side effect of this
placement is a small window in which hotplug sequence detection can trigger
unnecessarily, which isn't critical.
Move check_hotplug_seq() invocation to the same cpus_read_lock() block as
the hotplug operation enablement to close the window and get the invocation
out of the way for planned locking updates.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: David Vernet <void@manifault.com>
While bypassing, tasks are scheduled in FIFO order which favors tasks that
hog CPUs. This can slow down e.g. unloading of the BPF scheduler. While
bypassing, guaranteeing timely forward progress is the main goal. There's no
point in giving long slices. Shorten the time slice used while bypassing
from 20ms to 5ms.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>
In the bypass mode, the global DSQ is used to schedule all tasks in simple
FIFO order. All tasks are queued into the global DSQ and all CPUs try to
execute tasks from it. This creates a lot of cross-node cacheline accesses
and scheduling across the node boundaries, and can lead to live-lock
conditions where the system takes tens of minutes to disable the BPF
scheduler while executing in the bypass mode.
Split the global DSQ per NUMA node. Each node has its own global DSQ. When a
task is dispatched to SCX_DSQ_GLOBAL, it's put into the global DSQ local to
the task's CPU and all CPUs in a node only consume its node-local global
DSQ.
This resolves a livelock condition which could be reliably triggered on an
2x EPYC 7642 system by running `stress-ng --race-sched 1024` together with
`stress-ng --workload 80 --workload-threads 10` while repeatedly enabling
and disabling a SCX scheduler.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>
To prepare for the addition of find_global_dsq(). No functional changes.
Signed-off-by: tejun heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>
SCX_DSQ_GLOBAL is special in that it can't be used as a priority queue and
is consumed implicitly, but all BPF DSQ related kfuncs could be used on it.
SCX_DSQ_GLOBAL will be split per-node for scalability and those operations
won't make sense anymore. Disallow SCX_DSQ_GLOBAL on scx_bpf_consume(),
scx_bpf_dsq_nr_queued() and bpf_iter_scx_dsq_new(). This means that
SCX_DSQ_GLOBAL can only be used as a dispatch target from BPF schedulers.
With scx_flatcg, which was using SCX_DSQ_GLOBAL as the fallback DSQ,
updated, this shouldn't affect any schedulers.
This leaves find_dsq_for_dispatch() the only user of find_non_local_dsq().
Open code and remove find_non_local_dsq().
Signed-off-by: tejun heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>
move_remote_task_to_local_dsq() is only defined on SMP configs but
scx_disaptch_from_dsq() was calling move_remote_task_to_local_dsq() on UP
configs too causing build failures. Add a dummy
move_remote_task_to_local_dsq() which triggers a warning.
Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 4c30f5ce4f ("sched_ext: Implement scx_bpf_dispatch[_vtime]_from_dsq()")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202409241108.jaocHiDJ-lkp@intel.com/
As discussed during the distro-centric session within the sched_ext
Microconference at LPC 2024, introduce a sequence counter that is
incremented every time a BPF scheduler is loaded.
This feature can help distributions in diagnosing potential performance
regressions by identifying systems where users are running (or have ran)
custom BPF schedulers.
Example:
arighi@virtme-ng~> cat /sys/kernel/sched_ext/enable_seq
0
arighi@virtme-ng~> sudo scx_simple
local=1 global=0
^CEXIT: unregistered from user space
arighi@virtme-ng~> cat /sys/kernel/sched_ext/enable_seq
1
In this way user-space tools (such as Ubuntu's apport and similar) are
able to gather and include this information in bug reports.
Cc: Giovanni Gherdovich <giovanni.gherdovich@suse.com>
Cc: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Cc: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
Cc: Phil Auld <pauld@redhat.com>
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
Signed-off-by: Tejun Heo <tj@kernel.org>
a2f4b16e73 ("sched_ext: Build fix on !CONFIG_STACKTRACE[_SUPPORT]") tried
fixing build when !CONFIG_STACKTRACE but didn't so fully. Also put
stack_trace_print() and stack_trace_save() inside CONFIG_STACKTRACE to fix
build when !CONFIG_STACKTRACE.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202409220642.fDW2OmWc-lkp@intel.com/
A task moving across CPUs should not trigger quiescent/runnable task state
events as the task is staying runnable the whole time and just stopping and
then starting on different CPUs. Suppress quiescent/runnable task state
events if task_on_rq_migrating().
Signed-off-by: Tejun Heo <tj@kernel.org>
Suggested-by: David Vernet <void@manifault.com>
Cc: Daniel Hodges <hodges.daniel.scott@gmail.com>
Cc: Changwoo Min <multics69@gmail.com>
Cc: Andrea Righi <andrea.righi@linux.dev>
Cc: Dan Schatzberg <schatzberg.dan@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
While the BPF scheduler is being unloaded, the following warning messages
trigger sometimes:
NOHZ tick-stop error: local softirq work is pending, handler #80!!!
This is caused by the CPU entering idle while there are pending softirqs.
The main culprit is the bypassing state assertion not being synchronized
with rq operations. As the BPF scheduler cannot be trusted in the disable
path, the first step is entering the bypass mode where the BPF scheduler is
ignored and scheduling becomes global FIFO.
This is implemented by turning scx_ops_bypassing() true. However, the
transition isn't synchronized against anything and it's possible for enqueue
and dispatch paths to have different ideas on whether bypass mode is on.
Make each rq track its own bypass state with SCX_RQ_BYPASSING which is
modified while rq is locked.
This removes most of the NOHZ tick-stop messages but not completely. I
believe the stragglers are from the sched core bug where pick_task_scx() can
be called without preceding balance_scx(). Once that bug is fixed, we should
verify that all occurrences of this error message are gone too.
v2: scx_enabled() test moved inside the for_each_possible_cpu() loop so that
the per-cpu states are always synchronized with the global state.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: David Vernet <void@manifault.com>
