[Qemu-devel] [PATCH] PCI: minor performance optimization

[Cao jin <caoj.fnst@cn.fujitsu.com>]

1. Do param check in pci_add_capability2(), as it is a public API.
2. As spec says, each capability must be DWORD aligned, so an optimization can
   be done via Loop Unrolling.

Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
---
 hw/pci/pci.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index 168b9cc..1e99603 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -1924,13 +1924,15 @@ PCIDevice *pci_create_simple(PCIBus *bus, int devfn, const char *name)
 static uint8_t pci_find_space(PCIDevice *pdev, uint8_t size)
 {
     int offset = PCI_CONFIG_HEADER_SIZE;
-    int i;
-    for (i = PCI_CONFIG_HEADER_SIZE; i < PCI_CONFIG_SPACE_SIZE; ++i) {
+    int i = PCI_CONFIG_HEADER_SIZE;;
+
+    for (; i < PCI_CONFIG_SPACE_SIZE; i = i + 4) {
         if (pdev->used[i])
-            offset = i + 1;
-        else if (i - offset + 1 == size)
+            offset = i + 4;
+        else if (i - offset >= size)
             return offset;
     }
+
     return 0;
 }
 
@@ -2144,6 +2146,8 @@ int pci_add_capability2(PCIDevice *pdev, uint8_t cap_id,
     uint8_t *config;
     int i, overlapping_cap;
 
+    assert(size > 0);
+
     if (!offset) {
         offset = pci_find_space(pdev, size);
         if (!offset) {
-- 
2.1.0