[MIPS] SMTC: Instant IPI replay.

SMTC pseudo-interrupts between TCs are deferred and queued if the target
TC is interrupt-inhibited (IXMT). In the first SMTC prototypes, these
queued IPIs were serviced on return to user mode, or on entry into the
kernel idle loop. The INSTANT_REPLAY option dispatches them as part of
local_irq_restore() processing, which adds runtime overhead (hence the
option to turn it off), but ensures that IPIs are handled promptly even
under heavy I/O interrupt load.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 22 insertions, 0 deletions

diff --git a/include/asm-mips/irqflags.h b/include/asm-mips/irqflags.h
index 46bf5de5ac72..af3b07dfad4b 100644
--- a/include/asm-mips/irqflags.h
+++ b/include/asm-mips/irqflags.h
@@ -15,6 +15,27 @@
 
 #include <asm/hazards.h>
 
+/*
+ * CONFIG_MIPS_MT_SMTC_INSTANT_REPLAY does prompt replay of deferred IPIs,
+ * at the cost of branch and call overhead on each local_irq_restore()
+ */
+
+#ifdef CONFIG_MIPS_MT_SMTC_INSTANT_REPLAY
+
+extern void smtc_ipi_replay(void);
+
+#define irq_restore_epilog(flags)                               \
+do {                                                            \
+        if (!(flags & 0x0400))                                  \
+                smtc_ipi_replay();                              \
+} while (0)
+
+#else
+
+#define irq_restore_epilog(ignore) do { } while (0)
+
+#endif /* CONFIG_MIPS_MT_SMTC_INSTANT_REPLAY */
+
 __asm__ (
         "       .macro  raw_local_irq_enable                            \n"
         "       .set    push                                            \n"
@@ -193,6 +214,7 @@ do {									\
                 : "=r" (__tmp1)                                         \
                 : "0" (flags)                                           \
                 : "memory");                                            \
+        irq_restore_epilog(flags);                                      \
 } while(0)
 
 static inline int raw_irqs_disabled_flags(unsigned long flags)