From ce4e240c279a31096f74afa6584a62d64a1ba8c8 Mon Sep 17 00:00:00 2001 From: Suresh Siddha Date: Tue, 17 Mar 2009 10:16:54 -0800 Subject: x86: add x2apic_wrmsr_fence() to x2apic flush tlb paths Impact: optimize APIC IPI related barriers Uncached MMIO accesses for xapic are inherently serializing and hence we don't need explicit barriers for xapic IPI paths. x2apic MSR writes/reads don't have serializing semantics and hence need a serializing instruction or mfence, to make all the previous memory stores globally visisble before the x2apic msr write for IPI. Add x2apic_wrmsr_fence() in flush tlb path to x2apic specific paths. Signed-off-by: Suresh Siddha Cc: Peter Zijlstra Cc: Oleg Nesterov Cc: Jens Axboe Cc: Linus Torvalds Cc: "Paul E. McKenney" Cc: Rusty Russell Cc: Steven Rostedt Cc: "steiner@sgi.com" Cc: Nick Piggin LKML-Reference: <1237313814.27006.203.camel@localhost.localdomain> Signed-off-by: Ingo Molnar --- arch/x86/include/asm/apic.h | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'arch/x86/include') diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h index 6d5b6f0900e..00f5962d82d 100644 --- a/arch/x86/include/asm/apic.h +++ b/arch/x86/include/asm/apic.h @@ -108,6 +108,16 @@ extern void native_apic_icr_write(u32 low, u32 id); extern u64 native_apic_icr_read(void); #ifdef CONFIG_X86_X2APIC +/* + * Make previous memory operations globally visible before + * sending the IPI through x2apic wrmsr. We need a serializing instruction or + * mfence for this. + */ +static inline void x2apic_wrmsr_fence(void) +{ + asm volatile("mfence" : : : "memory"); +} + static inline void native_apic_msr_write(u32 reg, u32 v) { if (reg == APIC_DFR || reg == APIC_ID || reg == APIC_LDR || -- cgit v1.2.3-70-g09d2