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sched: Fix runtime accounting w/ split exec & sched contexts

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Without proxy-exec, we normally charge the "current" task for
both its vruntime as well as its sum_exec_runtime.

With proxy, however, we have two "current" contexts: the
scheduler context and the execution context. We want to charge
the execution context rq->curr (ie: proxy/lock holder) execution
time to its sum_exec_runtime (so it's clear to userland the
rq->curr task *is* running), as well as its thread group.

However the rest of the time accounting (such a vruntime and
cgroup accounting), we charge against the scheduler context
(rq->donor) task, because it is from that task that the time
is being "donated".

If the donor and curr tasks are the same, then it's the same as
without proxy.

Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Link: https://lkml.kernel.org/r/20250712033407.2383110-6-jstultz@google.com
This commit is contained in:
John Stultz
2025-07-12 03:33:46 +00:00
committed by Peter Zijlstra
parent 865d8cfb16
commit aa4f74dfd4
1 changed files with 28 additions and 14 deletions
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42
kernel/sched/fair.c
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@@ -1152,30 +1152,40 @@ void post_init_entity_util_avg(struct task_struct *p)
sa->runnable_avg = sa->util_avg;
}
static s64 update_curr_se(struct rq *rq, struct sched_entity *curr)
static s64 update_se(struct rq *rq, struct sched_entity *se)
{
u64 now = rq_clock_task(rq);
s64 delta_exec;
delta_exec = now - curr->exec_start;
delta_exec = now - se->exec_start;
if (unlikely(delta_exec <= 0))
return delta_exec;
curr->exec_start = now;
curr->sum_exec_runtime += delta_exec;
se->exec_start = now;
if (entity_is_task(se)) {
struct task_struct *donor = task_of(se);
struct task_struct *running = rq->curr;
/*
* If se is a task, we account the time against the running
* task, as w/ proxy-exec they may not be the same.
*/
running->se.exec_start = now;
running->se.sum_exec_runtime += delta_exec;
if (entity_is_task(curr)) {
struct task_struct *p = task_of(curr);
trace_sched_stat_runtime(running, delta_exec);
account_group_exec_runtime(running, delta_exec);
trace_sched_stat_runtime(p, delta_exec);
account_group_exec_runtime(p, delta_exec);
cgroup_account_cputime(p, delta_exec);
/* cgroup time is always accounted against the donor */
cgroup_account_cputime(donor, delta_exec);
} else {
/* If not task, account the time against donor se */
se->sum_exec_runtime += delta_exec;
}
if (schedstat_enabled()) {
struct sched_statistics *stats;
stats = __schedstats_from_se(curr);
stats = __schedstats_from_se(se);
__schedstat_set(stats->exec_max,
max(delta_exec, stats->exec_max));
}
@@ -1188,9 +1198,7 @@ static s64 update_curr_se(struct rq *rq, struct sched_entity *curr)
*/
s64 update_curr_common(struct rq *rq)
{
struct task_struct *donor = rq->donor;
return update_curr_se(rq, &donor->se);
return update_se(rq, &rq->donor->se);
}
/*
@@ -1198,6 +1206,12 @@ s64 update_curr_common(struct rq *rq)
*/
static void update_curr(struct cfs_rq *cfs_rq)
{
/*
* Note: cfs_rq->curr corresponds to the task picked to
* run (ie: rq->donor.se) which due to proxy-exec may
* not necessarily be the actual task running
* (rq->curr.se). This is easy to confuse!
*/
struct sched_entity *curr = cfs_rq->curr;
struct rq *rq = rq_of(cfs_rq);
s64 delta_exec;
@@ -1206,7 +1220,7 @@ static void update_curr(struct cfs_rq *cfs_rq)
if (unlikely(!curr))
return;
delta_exec = update_curr_se(rq, curr);
delta_exec = update_se(rq, curr);
if (unlikely(delta_exec <= 0))
return;