[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: Andi Kleen <ak@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/Kconfig b/net/sched/Kconfig
index 45d3bc0812c8b270ea95e7a6c21799d6ec42273b..81510da317924841131c74ab5bd31fa6cfe9eb8a 100644 (file)
--- a/net/sched/Kconfig
+++ b/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