linux-kernel - [PATCH] UV: cpu_relax in uv_wait

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Date:	Thu, 15 Jan 2009 09:51:20 -0600
From:	Cliff Wickman <cpw@....com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu
Subject: [PATCH] UV: cpu_relax in uv_wait_completion


From: Cliff Wickman <cpw@....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@....com>
Acked-by: Jack Steiner <steiner@....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;
 }
--
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