src/patches/suse-2.6.27.25/patches.fixes/ia64-configure-HAVE_UNSTABLE_SCHED_CLOCK-for-SGI_SN.patch

   1 Date: Tue, 6 Jan 2009 10:27:41 -0600
   2 From: Dimitri Sivanich <sivanich@sgi.com>
   3 To: linux-ia64@vger.kernel.org, Tony Luck <tony.luck@intel.com>,
   4         Greg KH <greg@kroah.com>
   5 Cc: linux-kernel@vger.kernel.org,
   6         Peter Zijlstra <peterz@infradead.org>,
   7         Gregory Haskins <ghaskins@novell.com>, Nick Piggin <npiggin@suse.de>,
   8         Tony Luck <tony.luck@gmail.com>, Robin Holt <holt@sgi.com>
   9 Subject: configure HAVE_UNSTABLE_SCHED_CLOCK for SGI_SN systems
  10
  11 Turn on CONFIG_HAVE_UNSTABLE_SCHED_CLOCK for SGI_SN.
  12
  13 SGI Altix has unsynchronized itc clocks.  This results in rq->clock
  14 occasionally being set to a time in the past by a remote cpu.
  15
  16 Note that it is possible that this problem may exist for other ia64
  17 machines as well, based on the following comment for sched_clock() in
  18 arch/ia64/kernel/head.S:
  19
  20  * Return a CPU-local timestamp in nano-seconds.  This timestamp is
  21  * NOT synchronized across CPUs its return value must never be
  22  * compared against the values returned on another CPU.  The usage in
  23  * kernel/sched.c ensures that.
  24
  25
  26 Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>
  27 Signed-off-by: Gregory Haskins <ghaskins@novell.com>
  28
  29 ---
  30
  31  arch/ia64/Kconfig |    1 +
  32  1 file changed, 1 insertion(+)
  33
  34 --- a/arch/ia64/Kconfig
  35 +++ b/arch/ia64/Kconfig
  36 @@ -504,6 +504,7 @@ config IA64_MC_ERR_INJECT
  37
  38  config SGI_SN
  39         def_bool y if (IA64_SGI_SN2 || IA64_GENERIC)
  40 +       select HAVE_UNSTABLE_SCHED_CLOCK
  41
  42  config IA64_ESI
  43         bool "ESI (Extensible SAL Interface) support"