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sched/fair: More complex proportional newidle balance

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It turns out that a few workloads (easyWave, fio) have a fairly low
success rate on newidle balance, but still benefit greatly from having
it anyway.

Luckliky these workloads have a faily low newidle rate, so the cost if
doing the newidle is relatively low, even if unsuccessfull.

Add a simple rate based part to the newidle ratio compute, such that
low rate newidle will still have a high newidle ratio.

This cures the easyWave and fio workloads while not affecting the
schbench numbers either (which have a very high newidle rate).

Reported-by: Mario Roy <marioeroy@gmail.com>
Reported-by: "Mohamed Abuelfotoh, Hazem" <abuehaze@amazon.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Mario Roy <marioeroy@gmail.com>
Tested-by: "Mohamed Abuelfotoh, Hazem" <abuehaze@amazon.com>
Link: https://patch.msgid.link/20260127151748.GA1079264@noisy.programming.kicks-ass.net
This commit is contained in:
Peter Zijlstra 2026-01-27 16:17:48 +01:00
parent 3b68df9781
commit 9fe89f022c
4 changed files with 30 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/sched/topology.h
View File

@ -95,6 +95,7 @@ struct sched_domain {
unsigned int newidle_call;
unsigned int newidle_success;
unsigned int newidle_ratio;
u64 newidle_stamp;
u64 max_newidle_lb_cost;
unsigned long last_decay_max_lb_cost;

27
kernel/sched/fair.c
View File

@ -12289,7 +12289,30 @@ static inline void update_newidle_stats(struct sched_domain *sd, unsigned int su
sd->newidle_success += success;
if (sd->newidle_call >= 1024) {
sd->newidle_ratio = sd->newidle_success;
u64 now = sched_clock();
s64 delta = now - sd->newidle_stamp;
sd->newidle_stamp = now;
int ratio = 0;
if (delta < 0)
delta = 0;
if (sched_feat(NI_RATE)) {
/*
* ratio delta freq
*
* 1024 - 4 s - 128 Hz
* 512 - 2 s - 256 Hz
* 256 - 1 s - 512 Hz
* 128 - .5 s - 1024 Hz
* 64 - .25 s - 2048 Hz
*/
ratio = delta >> 22;
}
ratio += sd->newidle_success;
sd->newidle_ratio = min(1024, ratio);
sd->newidle_call /= 2;
sd->newidle_success /= 2;
}
@ -12996,7 +13019,7 @@ static int sched_balance_newidle(struct rq *this_rq, struct rq_flags *rf)
if (sd->flags & SD_BALANCE_NEWIDLE) {
unsigned int weight = 1;
if (sched_feat(NI_RANDOM)) {
if (sched_feat(NI_RANDOM) && sd->newidle_ratio < 1024) {
/*
* Throw a 1k sided dice; and only run
* newidle_balance according to the success

1
kernel/sched/features.h
View File

@ -126,3 +126,4 @@ SCHED_FEAT(LATENCY_WARN, false)
* Do newidle balancing proportional to its success rate using randomization.
*/
SCHED_FEAT(NI_RANDOM, true)
SCHED_FEAT(NI_RATE, true)

3
kernel/sched/topology.c
View File

@ -4,6 +4,7 @@
*/
#include <linux/sched/isolation.h>
#include <linux/sched/clock.h>
#include <linux/bsearch.h>
#include "sched.h"
@ -1642,6 +1643,7 @@ sd_init(struct sched_domain_topology_level *tl,
struct sched_domain *sd = *per_cpu_ptr(sdd->sd, cpu);
int sd_id, sd_weight, sd_flags = 0;
struct cpumask *sd_span;
u64 now = sched_clock();
sd_weight = cpumask_weight(tl->mask(tl, cpu));
@ -1679,6 +1681,7 @@ sd_init(struct sched_domain_topology_level *tl,
.newidle_call = 512,
.newidle_success = 256,
.newidle_ratio = 512,
.newidle_stamp = now,
.max_newidle_lb_cost = 0,
.last_decay_max_lb_cost = jiffies,