[Xen-devel] [PATCH] linux/x86: Use cpu_relax() rather than barrier() in smp_call_function()

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

Short of getting an explanation for the odd difference to native, make
the code match native (and also, in the case of x86-64,
__smp_call_function_single()).

As usual, written and tested against 2.6.24-rc3 and made apply against
2.6.18 without further testing.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

Index: head-2007-11-30/arch/i386/kernel/smp-xen.c
===================================================================
--- head-2007-11-30.orig/arch/i386/kernel/smp-xen.c     2007-12-06 
14:56:17.000000000 +0100
+++ head-2007-11-30/arch/i386/kernel/smp-xen.c  2007-12-04 09:36:41.000000000 
+0100
@@ -525,11 +525,11 @@
 
        /* Wait for response */
        while (atomic_read(&data.started) != cpus)
-               barrier();
+               cpu_relax();
 
        if (wait)
                while (atomic_read(&data.finished) != cpus)
-                       barrier();
+                       cpu_relax();
        spin_unlock(&call_lock);
 
        return 0;
Index: head-2007-11-30/arch/x86_64/kernel/smp-xen.c
===================================================================
--- head-2007-11-30.orig/arch/x86_64/kernel/smp-xen.c   2007-12-06 
14:56:17.000000000 +0100
+++ head-2007-11-30/arch/x86_64/kernel/smp-xen.c        2007-12-04 
09:38:48.000000000 +0100
@@ -404,21 +404,13 @@
 
        /* Wait for response */
        while (atomic_read(&data.started) != cpus)
-#ifndef CONFIG_XEN
                cpu_relax();
-#else
-               barrier();
-#endif
 
        if (!wait)
                return;
 
        while (atomic_read(&data.finished) != cpus)
-#ifndef CONFIG_XEN
                cpu_relax();
-#else
-               barrier();
-#endif
 }
 
 /*




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