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>

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 2d802e9..55445f1 100644 (file)
--- 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? */