[PATCH 17/15] [HACK] futex: Force futex hash collision
From: Peter Zijlstra <peterz@infradead.org>
Date: 2023-09-22 20:59:50
Also in:
linux-arch, linux-mm, lkml
If you hate performance -- use this. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- kernel/futex/core.c | 6 ++++++ kernel/sched/features.h | 2 ++ 2 files changed, 8 insertions(+)
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c@@ -128,6 +128,9 @@ static int futex_put_value(u32 val, u32 } } +#include <linux/sched/cputime.h> +#include "../sched/sched.h" + /** * futex_hash - Return the hash bucket in the global hash * @key: Pointer to the futex key for which the hash is calculated
@@ -159,6 +162,9 @@ struct futex_hash_bucket *futex_hash(uni } } + if (sched_feat(FUTEX_SQUASH)) + hash = 0; + return &futex_queues[node][hash & (futex_hashsize - 1)]; } --- a/kernel/sched/features.h +++ b/kernel/sched/features.h
@@ -89,3 +89,5 @@ SCHED_FEAT(UTIL_EST_FASTUP, true) SCHED_FEAT(LATENCY_WARN, false) SCHED_FEAT(HZ_BW, true) + +SCHED_FEAT(FUTEX_SQUASH, false)