[PATCH 17/15] [HACK] futex: Force futex hash collision

[Peter Zijlstra]

If you hate performance -- use this.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 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)