x86, sparseirq: clean up Kconfig entry

Impact: improve help text
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/Kconfig

@@ -242,10 +242,14 @@ config SPARSE_IRQ
 	bool "Support sparse irq numbering"
 	depends on PCI_MSI || HT_IRQ
 	help
-	  This enables support for sparse irq, esp for msi/msi-x. You may need
-	  if you have lots of cards supports msi-x installed.
+	  This enables support for sparse irqs. This is useful for distro
+	  kernels that want to define a high CONFIG_NR_CPUS value but still
+	  want to have low kernel memory footprint on smaller machines.
 
-	  If you don't know what to do here, say Y.
+	  ( Sparse IRQs can also be beneficial on NUMA boxes, as they spread
+	    out the irq_desc[] array in a more NUMA-friendly way. )
+
+	  If you don't know what to do here, say N.
 
 config NUMA_MIGRATE_IRQ_DESC
 	bool "Move irq desc when changing irq smp_affinity"