From: Cliff Wickman <cpw@sgi.com>
Date: Thu, 15 Jan 2009 15:51:20 +0000 (-0600)
Subject: x86, UV: cpu_relax in uv_wait_completion
X-Git-Tag: v2.6.29-rc3~42^2~24
X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=18c07cf530cf4aa8b7551801f68ed40db5ee4e45;p=linux-2.6-omap-h63xx.git

x86, UV: cpu_relax in uv_wait_completion

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>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---

diff --git a/arch/x86/kernel/tlb_uv.c b/arch/x86/kernel/tlb_uv.c
index f885023167e..6812b829ed8 100644
--- a/arch/x86/kernel/tlb_uv.c
+++ b/arch/x86/kernel/tlb_uv.c
@@ -200,6 +200,7 @@ static int uv_wait_completion(struct bau_desc *bau_desc,
 				destination_timeouts = 0;
 			}
 		}
+		cpu_relax();
 	}
 	return FLUSH_COMPLETE;
 }