x86/IO-APIC: Drop function pointers from __ioapic_{read,write}_entry()

Function pointers are expensive, and the raw parameter is a constant at the
root of all call trees, meaning that it predicts very well with local branch
history.

Furthermore, the knock-on effects are quite impressive.

  $ ../scripts/bloat-o-meter xen-syms-before xen-syms-after
  add/remove: 0/4 grow/shrink: 3/9 up/down: 459/-823 (-364)
  Function                                     old     new   delta
  __ioapic_write_entry                          73     286    +213
  __ioapic_read_entry                           75     276    +201
  save_IO_APIC_setup                           182     227     +45
  eoi_IO_APIC_irq                              241     229     -12
  disable_IO_APIC                              296     280     -16
  mask_IO_APIC_setup                           272     240     -32
  __io_apic_write                               46       -     -46
  __io_apic_read                                46       -     -46
  io_apic_set_pci_routing                      985     930     -55
  __io_apic_eoi.part                           223     161     -62
  io_apic_write                                 69       -     -69
  io_apic_read                                  69       -     -69
  restore_IO_APIC_setup                        325     253     -72
  ioapic_guest_write                          1413    1333     -80
  clear_IO_APIC_pin                            447     343    -104
  setup_IO_APIC                               5148    4988    -160

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/arch/x86/io_apic.c b/xen/arch/x86/io_apic.c
index c3ad9efac88d2151b3f23357facc19aaa4830e27..1c49a0fe1478cd68c35ca0c9289d653fa932e941 100644 (file)
--- a/xen/arch/x86/io_apic.c
+++ b/xen/arch/x86/io_apic.c
@@ -235,11 +235,19 @@ union entry_union {
 struct IO_APIC_route_entry __ioapic_read_entry(
     unsigned int apic, unsigned int pin, bool raw)
 {
-    unsigned int (*read)(unsigned int, unsigned int)
-        = raw ? __io_apic_read : io_apic_read;
     union entry_union eu;
-    eu.w1 = (*read)(apic, 0x10 + 2 * pin);
-    eu.w2 = (*read)(apic, 0x11 + 2 * pin);
+
+    if ( raw )
+    {
+        eu.w1 = __io_apic_read(apic, 0x10 + 2 * pin);
+        eu.w2 = __io_apic_read(apic, 0x11 + 2 * pin);
+    }
+    else
+    {
+        eu.w1 = io_apic_read(apic, 0x10 + 2 * pin);
+        eu.w2 = io_apic_read(apic, 0x11 + 2 * pin);
+    }
+
     return eu.entry;
 }
 
@@ -259,12 +267,18 @@ void __ioapic_write_entry(
     unsigned int apic, unsigned int pin, bool raw,
     struct IO_APIC_route_entry e)
 {
-    void (*write)(unsigned int, unsigned int, unsigned int)
-        = raw ? __io_apic_write : io_apic_write;
     union entry_union eu = { .entry = e };
 
-    (*write)(apic, 0x11 + 2*pin, eu.w2);
-    (*write)(apic, 0x10 + 2*pin, eu.w1);
+    if ( raw )
+    {
+        __io_apic_write(apic, 0x11 + 2 * pin, eu.w2);
+        __io_apic_write(apic, 0x10 + 2 * pin, eu.w1);
+    }
+    else
+    {
+        io_apic_write(apic, 0x11 + 2 * pin, eu.w2);
+        io_apic_write(apic, 0x10 + 2 * pin, eu.w1);
+    }
 }
 
 static void ioapic_write_entry(