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sched/fair: Fix lag clamp

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Vincent reported that he was seeing undue lag clamping in a mixed
slice workload. Implement the max_slice tracking as per the todo
comment.

Fixes: 147f3efaa2 ("sched/fair: Implement an EEVDF-like scheduling policy")
Reported-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Vincent Guittot <vincent.guittot@linaro.org>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Tested-by: Shubhang Kaushik <shubhang@os.amperecomputing.com>
Link: https://patch.msgid.link/20250422101628.GA33555@noisy.programming.kicks-ass.net
This commit is contained in:
Peter Zijlstra 2025-04-22 12:16:28 +02:00
parent ff38424030
commit 6e3c0a4e1a
2 changed files with 36 additions and 4 deletions
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1
include/linux/sched.h
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@ -579,6 +579,7 @@ struct sched_entity {
u64 deadline;
u64 min_vruntime;
u64 min_slice;
u64 max_slice;
struct list_head group_node;
unsigned char on_rq;

39
kernel/sched/fair.c
View File

@ -748,6 +748,8 @@ u64 avg_vruntime(struct cfs_rq *cfs_rq)
return cfs_rq->zero_vruntime;
}
static inline u64 cfs_rq_max_slice(struct cfs_rq *cfs_rq);
/*
* lag_i = S - s_i = w_i * (V - v_i)
*
@ -761,17 +763,16 @@ u64 avg_vruntime(struct cfs_rq *cfs_rq)
* EEVDF gives the following limit for a steady state system:
*
* -r_max < lag < max(r_max, q)
*
* XXX could add max_slice to the augmented data to track this.
*/
static void update_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
u64 max_slice = cfs_rq_max_slice(cfs_rq) + TICK_NSEC;
s64 vlag, limit;
WARN_ON_ONCE(!se->on_rq);
vlag = avg_vruntime(cfs_rq) - se->vruntime;
limit = calc_delta_fair(max_t(u64, 2*se->slice, TICK_NSEC), se);
limit = calc_delta_fair(max_slice, se);
se->vlag = clamp(vlag, -limit, limit);
}
@ -829,6 +830,21 @@ static inline u64 cfs_rq_min_slice(struct cfs_rq *cfs_rq)
return min_slice;
}
static inline u64 cfs_rq_max_slice(struct cfs_rq *cfs_rq)
{
struct sched_entity *root = __pick_root_entity(cfs_rq);
struct sched_entity *curr = cfs_rq->curr;
u64 max_slice = 0ULL;
if (curr && curr->on_rq)
max_slice = curr->slice;
if (root)
max_slice = max(max_slice, root->max_slice);
return max_slice;
}
static inline bool __entity_less(struct rb_node *a, const struct rb_node *b)
{
return entity_before(__node_2_se(a), __node_2_se(b));
@ -853,6 +869,15 @@ static inline void __min_slice_update(struct sched_entity *se, struct rb_node *n
}
}
static inline void __max_slice_update(struct sched_entity *se, struct rb_node *node)
{
if (node) {
struct sched_entity *rse = __node_2_se(node);
if (rse->max_slice > se->max_slice)
se->max_slice = rse->max_slice;
}
}
/*
* se->min_vruntime = min(se->vruntime, {left,right}->min_vruntime)
*/
@ -860,6 +885,7 @@ static inline bool min_vruntime_update(struct sched_entity *se, bool exit)
{
u64 old_min_vruntime = se->min_vruntime;
u64 old_min_slice = se->min_slice;
u64 old_max_slice = se->max_slice;
struct rb_node *node = &se->run_node;
se->min_vruntime = se->vruntime;
@ -870,8 +896,13 @@ static inline bool min_vruntime_update(struct sched_entity *se, bool exit)
__min_slice_update(se, node->rb_right);
__min_slice_update(se, node->rb_left);
se->max_slice = se->slice;
__max_slice_update(se, node->rb_right);
__max_slice_update(se, node->rb_left);
return se->min_vruntime == old_min_vruntime &&
se->min_slice == old_min_slice;
se->min_slice == old_min_slice &&
se->max_slice == old_max_slice;
}
RB_DECLARE_CALLBACKS(static, min_vruntime_cb, struct sched_entity,