linux-kernel - [PATCH] irq: better struct irqaction layout

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Date:	Thu, 04 Nov 2010 11:13:48 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH] irq: better struct irqaction layout

We currently use kmalloc-96 slab for struct irqaction allocations on
64bit arches.

This is unfortunate because of possible false sharing and two cache
lines accesses.

Move 'name' and 'dir' fields at the end of the structure, and force a
suitable alignement.

Hot path fields now use one cache line on x86_64.

Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Andi Kleen <andi@...stfloor.org>
Cc: Peter Zijlstra <peterz@...radead.org>
---
 include/linux/interrupt.h |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 79d0c4f..55e0d42 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -114,15 +114,15 @@ typedef irqreturn_t (*irq_handler_t)(int, void *);
 struct irqaction {
 	irq_handler_t handler;
 	unsigned long flags;
-	const char *name;
 	void *dev_id;
 	struct irqaction *next;
 	int irq;
-	struct proc_dir_entry *dir;
 	irq_handler_t thread_fn;
 	struct task_struct *thread;
 	unsigned long thread_flags;
-};
+	const char *name;
+	struct proc_dir_entry *dir;
+} ____cacheline_internodealigned_in_smp;
 
 extern irqreturn_t no_action(int cpl, void *dev_id);
 


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