[PATCH] x86/x86_64: deferred handling of writes to /proc/irqxx/smp_affinity

When handling writes to /proc/irq, current code is re-programming rte
entries directly. This is not recommended and could potentially cause
chipset's to lockup, or cause missing interrupts.

CONFIG_IRQ_BALANCE does this correctly, where it re-programs only when the
interrupt is pending. The same needs to be done for /proc/irq handling as well.
Otherwise user space irq balancers are really not doing the right thing.

- Changed pending_irq_balance_cpumask to pending_irq_migrate_cpumask for
  lack of a generic name.
- added move_irq out of IRQ_BALANCE, and added this same to X86_64
- Added new proc handler for write, so we can do deferred write at irq
  handling time.
- Display of /proc/irq/XX/smp_affinity used to display CPU_MASKALL, instead
  it now shows only active cpu masks, or exactly what was set.
- Provided a common move_irq implementation, instead of duplicating
  when using generic irq framework.

Tested on i386/x86_64 and ia64 with CONFIG_PCI_MSI turned on and off.
Tested UP builds as well.

MSI testing: tbd: I have cards, need to look for a x-over cable, although I
did test an earlier version of this patch.  Will test in a couple days.

Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Acked-by: Zwane Mwaikambo <zwane@holomorphy.com>
Grudgingly-acked-by: Andi Kleen <ak@muc.de>
Signed-off-by: Coywolf Qi Hunt <coywolf@lovecn.org>
Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 12 insertions, 2 deletions

diff --git a/kernel/irq/proc.c b/kernel/irq/proc.c
index 85d08daa660..f26e534c658 100644
--- a/kernel/irq/proc.c
+++ b/kernel/irq/proc.c
@@ -19,12 +19,22 @@ static struct proc_dir_entry *root_irq_dir, *irq_dir[NR_IRQS];
  */
 static struct proc_dir_entry *smp_affinity_entry[NR_IRQS];
 
-void __attribute__((weak))
-proc_set_irq_affinity(unsigned int irq, cpumask_t mask_val)
+#ifdef CONFIG_GENERIC_PENDING_IRQ
+void proc_set_irq_affinity(unsigned int irq, cpumask_t mask_val)
+{
+        /*
+         * Save these away for later use. Re-progam when the
+         * interrupt is pending
+         */
+        set_pending_irq(irq, mask_val);
+}
+#else
+void proc_set_irq_affinity(unsigned int irq, cpumask_t mask_val)
 {
         irq_affinity[irq] = mask_val;
         irq_desc[irq].handler->set_affinity(irq, mask_val);
 }
+#endif
 
 static int irq_affinity_read_proc(char *page, char **start, off_t off,
                                   int count, int *eof, void *data)