Date: Tue, 6 Jan 2009 10:27:41 -0600 From: Dimitri Sivanich To: linux-ia64@vger.kernel.org, Tony Luck , Greg KH Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , Gregory Haskins , Nick Piggin , Tony Luck , Robin Holt Subject: configure HAVE_UNSTABLE_SCHED_CLOCK for SGI_SN systems Patch-mainline: not yet Turn on CONFIG_HAVE_UNSTABLE_SCHED_CLOCK for SGI_SN. SGI Altix has unsynchronized itc clocks. This results in rq->clock occasionally being set to a time in the past by a remote cpu. Note that it is possible that this problem may exist for other ia64 machines as well, based on the following comment for sched_clock() in arch/ia64/kernel/head.S: * Return a CPU-local timestamp in nano-seconds. This timestamp is * NOT synchronized across CPUs its return value must never be * compared against the values returned on another CPU. The usage in * kernel/sched.c ensures that. Signed-off-by: Dimitri Sivanich Signed-off-by: Gregory Haskins --- arch/ia64/Kconfig | 1 + 1 file changed, 1 insertion(+) --- a/arch/ia64/Kconfig +++ b/arch/ia64/Kconfig @@ -545,6 +545,7 @@ config IA64_MC_ERR_INJECT config SGI_SN def_bool y if (IA64_SGI_SN2 || IA64_GENERIC) + select HAVE_UNSTABLE_SCHED_CLOCK config IA64_ESI bool "ESI (Extensible SAL Interface) support"