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scx_rustland: provide get/set_cpu_owner()

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Provide the following primitives to get and set CPU ownership in the BPF
part. This improves code readability and these primitives can be used by
the BPF part as a baseline to implement a better CPU idle tracking in
the future.

Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
This commit is contained in:
Andrea Righi 2023-12-25 15:45:15 +01:00
parent cd7e1c6248
commit 7d01be9568
1 changed files with 39 additions and 18 deletions
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57
scheds/rust/scx_rustland/src/bpf/main.bpf.c
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@ -148,6 +148,40 @@ struct {
__type(value, u32);
} cpu_map SEC(".maps");
/*
* Assign a task to a CPU (used in .running() and .stopping()).
*
* If pid == 0 the CPU will be considered idle.
*/
static void set_cpu_owner(u32 cpu, u32 pid)
{
u32 *owner;
owner = bpf_map_lookup_elem(&cpu_map, &cpu);
if (!owner) {
scx_bpf_error("Failed to look up cpu_map for cpu %u", cpu);
return;
}
*owner= pid;
}
/*
* Get the pid of the task that is currently running on @cpu.
*
* Return 0 if the CPU is idle.
*/
static u32 get_cpu_owner(u32 cpu)
{
u32 *owner;
owner = bpf_map_lookup_elem(&cpu_map, &cpu);
if (!owner) {
scx_bpf_error("Failed to look up cpu_map for cpu %u", cpu);
return 0;
}
return *owner;
}
/*
* Return true if the target task @p is the user-space scheduler.
*/
@ -225,9 +259,6 @@ static void dispatch_global(struct task_struct *p, u64 enq_flags)
* If the CPU where the task was running is still idle, then the task can be
* dispatched immediately on the same CPU from .enqueue(), without having to
* call the scheduler.
*
* In the future we may want to improve this part and figure out a way to move
* this logic into the user-space scheduler as well.
*/
s32 BPF_STRUCT_OPS(rustland_select_cpu, struct task_struct *p, s32 prev_cpu,
u64 wake_flags)
@ -243,11 +274,11 @@ s32 BPF_STRUCT_OPS(rustland_select_cpu, struct task_struct *p, s32 prev_cpu,
* Always try to keep the tasks on the same CPU (unless the user-space
* scheduler decides otherwise).
*
* Then check if the previously used CPU is still idle, in this case we
* can dispatch directly from .enqueue() bypassing the user-space
* Check if the previously used CPU is idle, in this case we can
* dispatch directly from .enqueue(), bypassing the user-space
* scheduler.
*/
tctx->force_local = scx_bpf_test_and_clear_cpu_idle(prev_cpu);
tctx->force_local = get_cpu_owner(prev_cpu) == 0;
return prev_cpu;
}
@ -412,25 +443,15 @@ void BPF_STRUCT_OPS(rustland_dispatch, s32 cpu, struct task_struct *prev)
/* Task @p starts on a CPU */
void BPF_STRUCT_OPS(rustland_running, struct task_struct *p)
{
u32 key = scx_bpf_task_cpu(p);
u32 *value;
dbg_msg("start: pid=%d (%s)", p->pid, p->comm);
value = bpf_map_lookup_elem(&cpu_map, &key);
if (value)
*value = p->pid;
set_cpu_owner(scx_bpf_task_cpu(p), p->pid);
}
/* Task @p releases a CPU */
void BPF_STRUCT_OPS(rustland_stopping, struct task_struct *p, bool runnable)
{
u32 key = scx_bpf_task_cpu(p);
u32 *value;
dbg_msg("stop: pid=%d (%s)", p->pid, p->comm);
value = bpf_map_lookup_elem(&cpu_map, &key);
if (value)
*value = 0;
set_cpu_owner(scx_bpf_task_cpu(p), 0);
}
/* Task @p is created */