[PATCH] x86_64: Use cpu_relax in poll loop in GART IOMMU

The code waits for the GART to clear the TLB flush bit. Use cpu_relax
in this time to allow hypervisors to yield the CPU in this time.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/arch/x86_64/kernel/pci-gart.c b/arch/x86_64/kernel/pci-gart.c
index 0c3f052..ebd125e 100644 (file)
--- a/arch/x86_64/kernel/pci-gart.c
+++ b/arch/x86_64/kernel/pci-gart.c
@@ -148,9 +148,12 @@ static void flush_gart(struct device *dev)
                        if (!northbridges[i])
                                continue;
                        /* Make sure the hardware actually executed the flush. */
-                       do { 
+                       for (;;) { 
                                pci_read_config_dword(northbridges[i], 0x9c, &w);
-                       } while (w & 1);
+                               if (!(w & 1))
+                                       break;
+                               cpu_relax();
+                       }
                } 
                if (!flushed) 
                        printk("nothing to flush?\n");