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sched/fair: Add sched_smt_active check for fastpaths

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For fastpaths such as wakeup and load balance even minimal code additions
can add up. is_core_idle is accessed during load balance.

Other callsites of is_core_idle make sched_smt_active() check first.
Make the same check in should_we_balance.

Rest of access to cpu_smt_mask isn't in fastpath.

Note: Remove the stale comment above is_core_idle. Enqueue methods
of fair aren't close to it anymore.

Suggested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Link: https://patch.msgid.link/20260515172456.542799-4-sshegde@linux.ibm.com
This commit is contained in:
Shrikanth Hegde
2026-05-15 22:54:55 +05:30
committed by Peter Zijlstra
parent 5bc6ab2d42
commit 3dbb362f90
1 changed files with 4 additions and 5 deletions
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9
kernel/sched/fair.c
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@@ -1549,10 +1549,7 @@ update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
se->exec_start = rq_clock_task(rq_of(cfs_rq));
}
/**************************************************
* Scheduling class queueing methods:
*/
/* Check sched_smt_active before calling this to avoid overheads in fastpaths */
static inline bool is_core_idle(int cpu)
{
int sibling;
@@ -11961,7 +11958,9 @@ static int should_we_balance(struct lb_env *env)
* balancing cores, but remember the first idle SMT CPU for
* later consideration. Find CPU on an idle core first.
*/
if (!(env->sd->flags & SD_SHARE_CPUCAPACITY) && !is_core_idle(cpu)) {
if (sched_smt_active() &&
!(env->sd->flags & SD_SHARE_CPUCAPACITY) &&
!is_core_idle(cpu)) {
if (idle_smt == -1)
idle_smt = cpu;
/*