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Message-Id: <20230922205450.033535181@infradead.org>
Date: Fri, 22 Sep 2023 22:01:23 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: tglx@...utronix.de, axboe@...nel.dk
Cc: linux-kernel@...r.kernel.org, peterz@...radead.org,
mingo@...hat.com, dvhart@...radead.org, dave@...olabs.net,
andrealmeid@...lia.com, Andrew Morton <akpm@...ux-foundation.org>,
urezki@...il.com, hch@...radead.org, lstoakes@...il.com,
Arnd Bergmann <arnd@...db.de>, linux-api@...r.kernel.org,
linux-mm@...ck.org, linux-arch@...r.kernel.org,
malteskarupke@....de, steve.shaw@...el.com,
marko.makela@...iadb.com, andrei.artemev@...el.com
Subject: [PATCH 17/15] [HACK] futex: Force futex hash collision
If you hate performance -- use this.
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.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)
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