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scx_lavd: for a forked task, inherit its parent's statistics

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The old approach was too conservative in running a new task, so when a
fork-heavy workload competes with a CPU-bound workload, the fork-heavy
one is starved. The new approach solves the starvation problem by
inheriting parent's statistics. It seems a good (at least better than
old) guess how a new task will behave.

Signed-off-by: Changwoo Min <changwoo@igalia.com>
This commit is contained in:
Changwoo Min 2024-06-26 19:00:10 +09:00
parent ac9c49f5b5
commit abc6e31fef
1 changed files with 39 additions and 11 deletions
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50
scheds/rust/scx_lavd/src/bpf/main.bpf.c
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@ -2867,11 +2867,47 @@ void BPF_STRUCT_OPS(lavd_update_idle, s32 cpu, bool idle)
} }
} }
static void init_task_ctx(struct task_struct *p, struct task_ctx *taskc)
{
struct task_struct *parent;
struct task_ctx *taskc_parent;
u64 now;
/*
* Inherit parent's statistics if the parent is also under scx.
*/
parent = p->parent;
taskc_parent = try_get_task_ctx(parent);
if (parent && taskc_parent)
memcpy(taskc, taskc_parent, sizeof(*taskc));
else {
/*
* If parent's ctx does not exist, init some fields with
* reasonable defaults.
*/
taskc->run_time_ns = LAVD_SLICE_MIN_NS;
taskc->lat_prio = get_nice_prio(p);
taskc->run_freq = 1;
}
/*
* Reset context for a fresh new task.
*/
now = bpf_ktime_get_ns();
taskc->last_runnable_clk = now;
taskc->last_running_clk = now;
taskc->last_stopping_clk = now;
taskc->last_quiescent_clk = now;
taskc->greedy_ratio = 1000;
taskc->victim_cpu = (s32)LAVD_CPU_ID_NONE;
taskc->acc_run_time_ns = 0;
taskc->slice_ns = 0;
}
s32 BPF_STRUCT_OPS(lavd_init_task, struct task_struct *p, s32 BPF_STRUCT_OPS(lavd_init_task, struct task_struct *p,
struct scx_init_task_args *args) struct scx_init_task_args *args)
{ {
struct task_ctx *taskc; struct task_ctx *taskc;
u64 now;
/* /*
* When @p becomes under the SCX control (e.g., being forked), @p's * When @p becomes under the SCX control (e.g., being forked), @p's
@ -2887,17 +2923,9 @@ s32 BPF_STRUCT_OPS(lavd_init_task, struct task_struct *p,
/* /*
* Initialize @p's context with the current clock and default load. * Initialize @p's context.
*/ */
now = bpf_ktime_get_ns(); init_task_ctx(p, taskc);
taskc->last_runnable_clk = now;
taskc->last_running_clk = now;
taskc->last_stopping_clk = now;
taskc->last_quiescent_clk = now;
taskc->greedy_ratio = 1000;
taskc->run_time_ns = LAVD_LC_RUNTIME_MAX;
taskc->run_freq = 1;
taskc->victim_cpu = (s32)LAVD_CPU_ID_NONE;
/* /*
* When a task is forked, we immediately reflect changes to the current * When a task is forked, we immediately reflect changes to the current