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From: Peter Zijlstra <peterz@infradead.org>
To: tglx@linutronix.de, axboe@kernel.dk
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org,
	mingo@redhat.com, dvhart@infradead.org, dave@stgolabs.net,
	andrealmeid@igalia.com, Andrew Morton <akpm@linux-foundation.org>,
	urezki@gmail.com, hch@infradead.org, lstoakes@gmail.com,
	Arnd Bergmann <arnd@arndb.de>,
	linux-api@vger.kernel.org, linux-mm@kvack.org,
	linux-arch@vger.kernel.org, malteskarupke@web.de,
	steve.shaw@intel.com, marko.makela@mariadb.com,
	andrei.artemev@intel.com
Subject: [PATCH 17/15] [HACK] futex: Force futex hash collision
Date: Fri, 22 Sep 2023 22:01:23 +0200	[thread overview]
Message-ID: <20230922205450.033535181@infradead.org> (raw)
In-Reply-To: 20230922200120.011184118@infradead.org

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)



  parent reply	other threads:[~2023-09-22 20:59 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-09-21 10:45 [PATCH v3 00/15] futex: More futex2 bits peterz
2023-09-21 10:45 ` [PATCH v3 01/15] futex: Clarify FUTEX2 flags peterz
2023-09-21 17:36   ` [tip: locking/core] " tip-bot2 for peterz@infradead.org
2023-09-21 10:45 ` [PATCH v3 02/15] futex: Extend the " peterz
2023-09-21 17:36   ` [tip: locking/core] " tip-bot2 for peterz@infradead.org
2023-09-21 10:45 ` [PATCH v3 03/15] futex: Flag conversion peterz
2023-09-21 17:36   ` [tip: locking/core] " tip-bot2 for peterz@infradead.org
2023-09-21 10:45 ` [PATCH v3 04/15] futex: Validate futex value against futex size peterz
2023-09-21 17:36   ` [tip: locking/core] " tip-bot2 for peterz@infradead.org
2023-09-21 10:45 ` [PATCH v3 05/15] futex: Add sys_futex_wake() peterz
2023-09-21 17:36   ` [tip: locking/core] " tip-bot2 for peterz@infradead.org
2023-09-21 10:45 ` [PATCH v3 06/15] futex: FLAGS_STRICT peterz
2023-09-21 15:14   ` Thomas Gleixner
2023-09-21 17:36   ` [tip: locking/core] " tip-bot2 for peterz@infradead.org
2023-09-21 10:45 ` [PATCH v3 07/15] futex: Add sys_futex_wait() peterz
2023-09-21 17:36   ` [tip: locking/core] " tip-bot2 for peterz@infradead.org
2023-09-21 10:45 ` [PATCH v3 08/15] futex: Propagate flags into get_futex_key() peterz
2023-09-21 17:36   ` [tip: locking/core] " tip-bot2 for peterz@infradead.org
2023-09-21 10:45 ` [PATCH v3 09/15] futex: Add flags2 argument to futex_requeue() peterz
2023-09-21 17:36   ` [tip: locking/core] " tip-bot2 for peterz@infradead.org
2023-09-21 10:45 ` [PATCH v3 10/15] futex: Add sys_futex_requeue() peterz
2023-09-21 17:35   ` [tip: locking/core] " tip-bot2 for peterz@infradead.org
2023-09-22  9:35   ` [PATCH v3 10/15] " Ingo Molnar
2023-09-22 11:03     ` Peter Zijlstra
2023-09-22 13:56       ` Jens Axboe
2023-09-21 10:45 ` [PATCH v3 11/15] mm: Add vmalloc_huge_node() peterz
2023-09-21 10:45 ` [PATCH v3 12/15] futex: Implement FUTEX2_NUMA peterz
2023-09-21 10:45 ` [PATCH v3 13/15] futex: Propagate flags into futex_get_value_locked() peterz
2023-09-21 10:45 ` [PATCH v3 14/15] futex: Enable FUTEX2_{8,16} peterz
2023-09-21 10:45 ` [PATCH v3 15/15] futex,selftests: Extend the futex selftests peterz
2023-09-21 11:41   ` Peter Zijlstra
2023-09-22 20:01 ` futex2 numa stuff Peter Zijlstra
2023-09-22 20:01   ` [PATCH 15/15] futex,selftests: Extend the futex selftests Peter Zijlstra
2023-09-22 20:01   ` [PATCH 16/15] futex,selftests: Extend the futex selftests for NUMA Peter Zijlstra
2023-09-22 20:01   ` Peter Zijlstra [this message]
2023-09-28 13:40   ` futex2 numa stuff Davidlohr Bueso

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