[NET]: Disable NET_SCH_CLK_CPU for SMP x86 hosts

Opterons with frequency scaling have fully unsynchronized TSCs
running at different frequencies, so using TSCs there is not a good idea. 
Also some other x86 boxes have this problem. gettimeofday should be good 
enough, so just disable it.
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sched/Kconfig

@@ -72,9 +72,11 @@ config NET_SCH_CLK_GETTIMEOFDAY
 	  Choose this if you need a high resolution clock source but can't use
 	  the CPU's cycle counter.
 
+# don't allow on SMP x86 because they can have unsynchronized TSCs.
+# gettimeofday is a good alternative
 config NET_SCH_CLK_CPU
 	bool "CPU cycle counter"
-	depends on X86_TSC || X86_64 || ALPHA || SPARC64 || PPC64 || IA64
+	depends on ((X86_TSC || X86_64) && !SMP) || ALPHA || SPARC64 || PPC64 || IA64
 	help
 	  Say Y here if you want to use the CPU's cycle counter as clock source.
 	  This is a cheap and high resolution clock source, but on some