[PATCH] Avoid double flush in do_tlb_flush_all()

[PATCH] Avoid double flush in do_tlb_flush_all()

[Andi Kleen]

Avoid double flush in do_tlb_flush_all()

leave_mm already flushes the TLBs, so don't need to flush directly before that
in do_flush_tlb_all(). Avoid the double flush.

Pointed out by Rainer Weikusat

Signed-off-by: Andi Kleen <ak@linux.intel.com>

---
 arch/x86/kernel/tlb_32.c |    5 ++---
 arch/x86/kernel/tlb_64.c |    7 +++----
 2 files changed, 5 insertions(+), 7 deletions(-)

Index: linux-2.6.27-rc4-misc/arch/x86/kernel/tlb_32.c
===================================================================
--- linux-2.6.27-rc4-misc.orig/arch/x86/kernel/tlb_32.c
+++ linux-2.6.27-rc4-misc/arch/x86/kernel/tlb_32.c
@@ -229,11 +229,10 @@ EXPORT_SYMBOL(flush_tlb_page);
 
 static void do_flush_tlb_all(void *info)
 {
-	unsigned long cpu = smp_processor_id();
-
-	__flush_tlb_all();
 	if (per_cpu(cpu_tlbstate, cpu).state == TLBSTATE_LAZY)
 		leave_mm(cpu);
+	else
+		__flush_tlb_all(smp_processor_id());
 }
 
 void flush_tlb_all(void)
Index: linux-2.6.27-rc4-misc/arch/x86/kernel/tlb_64.c
===================================================================
--- linux-2.6.27-rc4-misc.orig/arch/x86/kernel/tlb_64.c
+++ linux-2.6.27-rc4-misc/arch/x86/kernel/tlb_64.c
@@ -266,11 +266,10 @@ void flush_tlb_page(struct vm_area_struc
 
 static void do_flush_tlb_all(void *info)
 {
-	unsigned long cpu = smp_processor_id();
-
-	__flush_tlb_all();
 	if (read_pda(mmu_state) == TLBSTATE_LAZY)
-		leave_mm(cpu);
+		leave_mm(smp_processor_id());
+	else
+		__flush_tlb_all();
 }
 
 void flush_tlb_all(void)

Re: [PATCH] Avoid double flush in do_tlb_flush_all()

[Arjan van de Ven]

On Sat, 30 Aug 2008 12:20:12 +0200
Andi Kleen <andi@firstfloor.org> wrote:

> Avoid double flush in do_tlb_flush_all()
> 
> leave_mm already flushes the TLBs, so don't need to flush directly
> before that in do_flush_tlb_all(). Avoid the double flush.

but... the leave_mm won't flush the global tlbs, while
__flush_tlb_all() does, right?

sounds like we do need the behavior