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Commit e729aa16 authored May 08, 2007 by Ravikiran G Thirumalai Committed by Linus Torvalds May 08, 2007

Pad irq_desc to internode cacheline size



We noticed a drop in n/w performance due to the irq_desc being cacheline
aligned rather than internode aligned.  We see 50% of expected performance
when two e1000 nics local to two different nodes have consecutive irq
descriptors allocated, due to false sharing.

Note that this patch does away with cacheline padding for the UP case, as
it does not seem useful for UP configurations.

Signed-off-by: Ravikiran Thirumalai <kiran@scalex86.org>
Signed-off-by: Shai Fultheim <shai@scalex86.org>
Cc: "Siddha, Suresh B" <suresh.b.siddha@intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 428e6ce0

include/linux/irq.h

+1 −3

Original line number	Original line	Diff line number	Diff line
	@@ -147,8 +147,6 @@ struct irq_chip {
	* @dir: /proc/irq/ procfs entry		* @dir: /proc/irq/ procfs entry
	* @affinity_entry: /proc/irq/smp_affinity procfs entry on SMP		* @affinity_entry: /proc/irq/smp_affinity procfs entry on SMP
	* @name: flow handler name for /proc/interrupts output		* @name: flow handler name for /proc/interrupts output
	*
	* Pad this out to 32 bytes for cache and indexing reasons.
	*/		*/
	struct irq_desc {		struct irq_desc {
	irq_flow_handler_t handle_irq;		irq_flow_handler_t handle_irq;
	@@ -175,7 +173,7 @@ struct irq_desc {
	struct proc_dir_entry *dir;		struct proc_dir_entry *dir;
	#endif		#endif
	const char *name;		const char *name;
	} ____cacheline_aligned;		} ____cacheline_internodealigned_in_smp;

	extern struct irq_desc irq_desc[NR_IRQS];		extern struct irq_desc irq_desc[NR_IRQS];

kernel/irq/handle.c

+1 −1

Original line number	Original line	Diff line number	Diff line
	@@ -48,7 +48,7 @@ handle_bad_irq(unsigned int irq, struct irq_desc *desc)
	*		*
	* Controller mappings for all interrupt sources:		* Controller mappings for all interrupt sources:
	*/		*/
	struct irq_desc irq_desc[NR_IRQS] __cacheline_aligned = {		struct irq_desc irq_desc[NR_IRQS] __cacheline_aligned_in_smp = {
	[0 ... NR_IRQS-1] = {		[0 ... NR_IRQS-1] = {
	.status = IRQ_DISABLED,		.status = IRQ_DISABLED,
	.chip = &no_irq_chip,		.chip = &no_irq_chip,