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authorTakuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>2012-09-05 19:30:01 +0900
committerMarcelo Tosatti <mtosatti@redhat.com>2012-09-12 13:38:23 -0300
commitecba9a52acdf20530d561b7634b80c35c308943a (patch)
tree8a8ef1bd20dd24b4181acab240906da6978c117f /arch/x86/kvm
parent7de5bdc96c372ab875408c86e0099958dba89f56 (diff)
downloadlinux-ecba9a52acdf20530d561b7634b80c35c308943a.tar.bz2
KVM: x86: lapic: Clean up find_highest_vector() and count_vectors()
find_highest_vector() and count_vectors(): - Instead of using magic values, define and use proper macros. find_highest_vector(): - Remove likely() which is there only for historical reasons and not doing correct branch predictions anymore. Using such heuristics to optimize this function is not worth it now. Let CPUs predict things instead. - Stop checking word[0] separately. This was only needed for doing likely() optimization. - Use for loop, not while, to iterate over the register array to make the code clearer. Note that we actually confirmed that the likely() did wrong predictions by inserting debug code. Acked-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Diffstat (limited to 'arch/x86/kvm')
-rw-r--r--arch/x86/kvm/lapic.c30
1 files changed, 18 insertions, 12 deletions
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 07ad628dadb7..6f9fd633c888 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -66,6 +66,7 @@
#define APIC_DEST_NOSHORT 0x0
#define APIC_DEST_MASK 0x800
#define MAX_APIC_VECTOR 256
+#define APIC_VECTORS_PER_REG 32
#define VEC_POS(v) ((v) & (32 - 1))
#define REG_POS(v) (((v) >> 5) << 4)
@@ -208,25 +209,30 @@ static const unsigned int apic_lvt_mask[APIC_LVT_NUM] = {
static int find_highest_vector(void *bitmap)
{
- u32 *word = bitmap;
- int word_offset = MAX_APIC_VECTOR >> 5;
+ int vec;
+ u32 *reg;
- while ((word_offset != 0) && (word[(--word_offset) << 2] == 0))
- continue;
+ for (vec = MAX_APIC_VECTOR - APIC_VECTORS_PER_REG;
+ vec >= 0; vec -= APIC_VECTORS_PER_REG) {
+ reg = bitmap + REG_POS(vec);
+ if (*reg)
+ return fls(*reg) - 1 + vec;
+ }
- if (likely(!word_offset && !word[0]))
- return -1;
- else
- return fls(word[word_offset << 2]) - 1 + (word_offset << 5);
+ return -1;
}
static u8 count_vectors(void *bitmap)
{
- u32 *word = bitmap;
- int word_offset;
+ int vec;
+ u32 *reg;
u8 count = 0;
- for (word_offset = 0; word_offset < MAX_APIC_VECTOR >> 5; ++word_offset)
- count += hweight32(word[word_offset << 2]);
+
+ for (vec = 0; vec < MAX_APIC_VECTOR; vec += APIC_VECTORS_PER_REG) {
+ reg = bitmap + REG_POS(vec);
+ count += hweight32(*reg);
+ }
+
return count;
}