[tip: sched/core] sched/fair: Use full weight to __calc_delta()

[tip-bot2 for Peter Zijlstra]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     db4551e2ba346663b7b16f0b5d36d308b615c50e
Gitweb:        https://git.kernel.org/tip/db4551e2ba346663b7b16f0b5d36d308b615c50e
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Wed, 11 Feb 2026 17:07:58 +01:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Mon, 23 Feb 2026 18:04:10 +01:00

sched/fair: Use full weight to __calc_delta()

Since we now use the full weight for avg_vruntime(), also make
__calc_delta() use the full value.

Since weight is effectively NICE_0_LOAD, this is 20 bits on 64bit.
This leaves 44 bits for delta_exec, which is ~16k seconds, way longer
than any one tick would ever be, so no worry about overflow.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Tested-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
Tested-by: Shubhang Kaushik <shubhang@xxxxxxxxxxxxxxxxxxxxxx>
Link: https://patch.msgid.link/20260219080625.183283814%40infradead.org
---
 kernel/sched/fair.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2b98054..23315c2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -225,6 +225,7 @@ void __init sched_init_granularity(void)
 	update_sysctl();
 }
 
+#ifndef CONFIG_64BIT
 #define WMULT_CONST	(~0U)
 #define WMULT_SHIFT	32
 
@@ -283,6 +284,12 @@ static u64 __calc_delta(u64 delta_exec, unsigned long weight, struct load_weight
 
 	return mul_u64_u32_shr(delta_exec, fact, shift);
 }
+#else
+static u64 __calc_delta(u64 delta_exec, unsigned long weight, struct load_weight *lw)
+{
+	return (delta_exec * weight) / lw->weight;
+}
+#endif
 
 /*
  * delta /= w