powerpc: Streamline ret_from_except_lite for non-iSeries platforms

There is a small passage of code in ret_from_except_lite which is
only required on iSeries.  For a multi-platform kernel on non-iSeries
machines this means we end up executing ~15 nops in ret_from_except_lite.

It would be nicer if non-iSeries could skip the code entirely, and on
iSeries we can jump out of line to execute the code.

I have no performance numbers to justify this, other than the assertion
that executing 15 nops takes longer than executing 0.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 29 insertions, 24 deletions

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 2d802e97097c..55445f1dba8a 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -512,31 +512,12 @@ _GLOBAL(ret_from_except_lite)
 #endif
 
 restore:
-        ld      r5,SOFTE(r1)
-#ifdef CONFIG_PPC_ISERIES
 BEGIN_FW_FTR_SECTION
-        cmpdi   0,r5,0
-        beq     4f
-        /* Check for pending interrupts (iSeries) */
-        ld      r3,PACALPPACAPTR(r13)
-        ld      r3,LPPACAANYINT(r3)
-        cmpdi   r3,0
-        beq+    4f                      /* skip do_IRQ if no interrupts */
-
-        li      r3,0
-        stb     r3,PACASOFTIRQEN(r13)   /* ensure we are soft-disabled */
-#ifdef CONFIG_TRACE_IRQFLAGS
-        bl      .trace_hardirqs_off
-        mfmsr   r10
-#endif
-        ori     r10,r10,MSR_EE
-        mtmsrd  r10                     /* hard-enable again */
-        addi    r3,r1,STACK_FRAME_OVERHEAD
-        bl      .do_IRQ
-        b       .ret_from_except_lite           /* loop back and handle more */
-4:
-END_FW_FTR_SECTION_IFSET(FW_FEATURE_ISERIES)
-#endif
+        ld      r5,SOFTE(r1)
+FW_FTR_SECTION_ELSE
+        b       iseries_check_pending_irqs
+ALT_FW_FTR_SECTION_END_IFCLR(FW_FEATURE_ISERIES)
+2:
         TRACE_AND_RESTORE_IRQ(r5);
 
         /* extract EE bit and use it to restore paca->hard_enabled */
@@ -592,6 +573,30 @@ END_FW_FTR_SECTION_IFSET(FW_FEATURE_ISERIES)
         rfid
         b       .       /* prevent speculative execution */
 
+iseries_check_pending_irqs:
+#ifdef CONFIG_PPC_ISERIES
+        ld      r5,SOFTE(r1)
+        cmpdi   0,r5,0
+        beq     2b
+        /* Check for pending interrupts (iSeries) */
+        ld      r3,PACALPPACAPTR(r13)
+        ld      r3,LPPACAANYINT(r3)
+        cmpdi   r3,0
+        beq+    2b                      /* skip do_IRQ if no interrupts */
+
+        li      r3,0
+        stb     r3,PACASOFTIRQEN(r13)   /* ensure we are soft-disabled */
+#ifdef CONFIG_TRACE_IRQFLAGS
+        bl      .trace_hardirqs_off
+        mfmsr   r10
+#endif
+        ori     r10,r10,MSR_EE
+        mtmsrd  r10                     /* hard-enable again */
+        addi    r3,r1,STACK_FRAME_OVERHEAD
+        bl      .do_IRQ
+        b       .ret_from_except_lite           /* loop back and handle more */
+#endif
+
 do_work:
 #ifdef CONFIG_PREEMPT
         andi.   r0,r3,MSR_PR    /* Returning to user mode? */