[PATCH] UV: cpu_relax in uv_wait_completion

[Cliff Wickman <cpw@sgi.com>]

From: Cliff Wickman <cpw@sgi.com>

The function uv_wait_completion() spins on reads of a memory-mapped
register, waiting for completion of BAU hardware replies.
It should call "cpu_relax()" between those reads to improve performance
on hyperthreaded configurations.

Signed-off-by: Cliff Wickman <cpw@sgi.com>
Acked-by: Jack Steiner <steiner@sgi.org>

---
 arch/x86/kernel/tlb_uv.c |    1 +
 1 file changed, 1 insertion(+)

Index: linux/arch/x86/kernel/tlb_uv.c
===================================================================
--- linux.orig/arch/x86/kernel/tlb_uv.c
+++ linux/arch/x86/kernel/tlb_uv.c
@@ -200,6 +200,7 @@ static int uv_wait_completion(struct bau
 				destination_timeouts = 0;
 			}
 		}
+		cpu_relax();
 	}
 	return FLUSH_COMPLETE;
 }