Function pointers are expensive, and the raw parameter is a constant from all
callers, 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.coop...@citrix.com>
---
CC: Jan Beulich <jbeul...@suse.com>
CC: Roger Pau Monné <roger....@citrix.com>
CC: Wei Liu <w...@xen.org>
---
xen/arch/x86/io_apic.c | 30 ++++++++++++++++++++++--------
1 file changed, 22 insertions(+), 8 deletions(-)
diff --git a/xen/arch/x86/io_apic.c b/xen/arch/x86/io_apic.c
index c3ad9efac88d..1c49a0fe1478 100644
--- 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(
--
2.11.0
