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sched_ext: Provide a sysfs enable_seq counter

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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>
This commit is contained in:
Andrea Righi 2024-09-21 21:39:21 +02:00 committed by Tejun Heo
parent 62d3726d4c
commit 431844b65f
3 changed files with 28 additions and 0 deletions
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10
Documentation/scheduler/sched-ext.rst
View File

@ -83,6 +83,15 @@ The current status of the BPF scheduler can be determined as follows:
# cat /sys/kernel/sched_ext/root/ops
simple
You can check if any BPF scheduler has ever been loaded since boot by examining
this monotonically incrementing counter (a value of zero indicates that no BPF
scheduler has been loaded):
.. code-block:: none
# cat /sys/kernel/sched_ext/enable_seq
1
``tools/sched_ext/scx_show_state.py`` is a drgn script which shows more
detailed information:
@ -96,6 +105,7 @@ detailed information:
enable_state : enabled (2)
bypass_depth : 0
nr_rejected : 0
enable_seq : 1
If ``CONFIG_SCHED_DEBUG`` is set, whether a given task is on sched_ext can
be determined as follows:

17
kernel/sched/ext.c
View File

@ -874,6 +874,13 @@ static struct scx_exit_info *scx_exit_info;
static atomic_long_t scx_nr_rejected = ATOMIC_LONG_INIT(0);
static atomic_long_t scx_hotplug_seq = ATOMIC_LONG_INIT(0);
/*
* A monotically increasing sequence number that is incremented every time a
* scheduler is enabled. This can be used by to check if any custom sched_ext
* scheduler has ever been used in the system.
*/
static atomic_long_t scx_enable_seq = ATOMIC_LONG_INIT(0);
/*
* The maximum amount of time in jiffies that a task may be runnable without
* being scheduled on a CPU. If this timeout is exceeded, it will trigger
@ -4154,11 +4161,19 @@ static ssize_t scx_attr_hotplug_seq_show(struct kobject *kobj,
}
SCX_ATTR(hotplug_seq);
static ssize_t scx_attr_enable_seq_show(struct kobject *kobj,
struct kobj_attribute *ka, char *buf)
{
return sysfs_emit(buf, "%ld\n", atomic_long_read(&scx_enable_seq));
}
SCX_ATTR(enable_seq);
static struct attribute *scx_global_attrs[] = {
&scx_attr_state.attr,
&scx_attr_switch_all.attr,
&scx_attr_nr_rejected.attr,
&scx_attr_hotplug_seq.attr,
&scx_attr_enable_seq.attr,
NULL,
};
@ -5177,6 +5192,8 @@ static int scx_ops_enable(struct sched_ext_ops *ops, struct bpf_link *link)
kobject_uevent(scx_root_kobj, KOBJ_ADD);
mutex_unlock(&scx_ops_enable_mutex);
atomic_long_inc(&scx_enable_seq);
return 0;
err_del:

1
tools/sched_ext/scx_show_state.py
View File

@ -37,3 +37,4 @@ print(f'switched_all : {read_static_key("__scx_switched_all")}')
print(f'enable_state : {ops_state_str(enable_state)} ({enable_state})')
print(f'bypass_depth : {read_atomic("scx_ops_bypass_depth")}')
print(f'nr_rejected : {read_atomic("scx_nr_rejected")}')
print(f'enable_seq : {read_atomic("scx_enable_seq")}')