x86/apic: Implement EIO micro-optimization

We know both register and value for eoi beforehand, so there's no need to check it and no need to do math to calculate the msr. Saves instructions/branches on each EOI when using x2apic. I looked at the objdump output to verify that the generated code looks right and actually is shorter. The real improvemements will be on the KVM guest side though, those come in a later patch. Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Cc: Avi Kivity <avi@redhat.com> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: gleb@redhat.com Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/e019d1a125316f10d3e3a4b2f6bda41473f4fb72.1337184153.git.mst@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
git-mirror · May 18, 2012 · 0ab711a · 0ab711a
1 parent 2a43195
commit 0ab711a
Show file tree

Hide file tree

Showing 4 changed files with 8 additions and 3 deletions.
diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
@@ -138,6 +138,11 @@ static inline void native_apic_msr_write(u32 reg, u32 v)
 	wrmsr(APIC_BASE_MSR + (reg >> 4), v, 0);
 }
 
+static inline void native_apic_msr_eoi_write(u32 reg, u32 v)
+{
+	wrmsr(APIC_BASE_MSR + (APIC_EOI >> 4), APIC_EOI_ACK, 0);
+}
+
 static inline u32 native_apic_msr_read(u32 reg)
 {
 	u64 msr;

diff --git a/arch/x86/kernel/apic/x2apic_cluster.c b/arch/x86/kernel/apic/x2apic_cluster.c
@@ -260,7 +260,7 @@ static struct apic apic_x2apic_cluster = {
 
 	.read				= native_apic_msr_read,
 	.write				= native_apic_msr_write,
-	.eoi_write			= native_apic_msr_write,
+	.eoi_write			= native_apic_msr_eoi_write,
 	.icr_read			= native_x2apic_icr_read,
 	.icr_write			= native_x2apic_icr_write,
 	.wait_icr_idle			= native_x2apic_wait_icr_idle,

diff --git a/arch/x86/kernel/apic/x2apic_phys.c b/arch/x86/kernel/apic/x2apic_phys.c
@@ -172,7 +172,7 @@ static struct apic apic_x2apic_phys = {
 
 	.read				= native_apic_msr_read,
 	.write				= native_apic_msr_write,
-	.eoi_write			= native_apic_msr_write,
+	.eoi_write			= native_apic_msr_eoi_write,
 	.icr_read			= native_x2apic_icr_read,
 	.icr_write			= native_x2apic_icr_write,
 	.wait_icr_idle			= native_x2apic_wait_icr_idle,

diff --git a/arch/x86/kernel/apic/x2apic_uv_x.c b/arch/x86/kernel/apic/x2apic_uv_x.c
@@ -404,7 +404,7 @@ static struct apic __refdata apic_x2apic_uv_x = {
 
 	.read				= native_apic_msr_read,
 	.write				= native_apic_msr_write,
-	.eoi_write			= native_apic_msr_write,
+	.eoi_write			= native_apic_msr_eoi_write,
 	.icr_read			= native_x2apic_icr_read,
 	.icr_write			= native_x2apic_icr_write,
 	.wait_icr_idle			= native_x2apic_wait_icr_idle,