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authorChristoph Lameter <clameter@sgi.com>2007-08-01 13:49:45 -0700
committerTony Luck <tony.luck@intel.com>2007-08-01 14:02:36 -0700
commitb718f91c14604e4ab5cdfe8d3baff8111425ea7d (patch)
treecd08e8af56d3d70c0b9b33255b3a44a7ce514a5e /arch
parent40d485753423b87239cc16b6c8141ef8792324d9 (diff)
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[IA64] ITC: Reduce rating for ITC clock if ITCs are drifty
Make sure to reduce the rating of the ITC clock if ITCs are drifty. If they are drifting then we have not synchronized the ITC values, nor are we doing the jitter compensation (useless since drift may increase the differentials arbitrarily). Without this patch it is possible that the ITC clock becomes selected as the system clock on systems with drifty ITCs which will result in nanosleep hanging. One can still select the itc clock manually on such systems via clocksource=itc (Produces nice hangs on SGI Altix.) Signed-off-by: Christoph Lameter <clameter@sgi.com> Signed-off-by: Tony Luck <tony.luck@intel.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/ia64/kernel/time.c16
1 files changed, 15 insertions, 1 deletions
diff --git a/arch/ia64/kernel/time.c b/arch/ia64/kernel/time.c
index 6c0e9e2e1b82..98cfc90cab1d 100644
--- a/arch/ia64/kernel/time.c
+++ b/arch/ia64/kernel/time.c
@@ -240,7 +240,21 @@ ia64_init_itm (void)
if (!nojitter)
itc_jitter_data.itc_jitter = 1;
#endif
- }
+ } else
+ /*
+ * ITC is drifty and we have not synchronized the ITCs in smpboot.c.
+ * ITC values may fluctuate significantly between processors.
+ * Clock should not be used for hrtimers. Mark itc as only
+ * useful for boot and testing.
+ *
+ * Note that jitter compensation is off! There is no point of
+ * synchronizing ITCs since they may be large differentials
+ * that change over time.
+ *
+ * The only way to fix this would be to repeatedly sync the
+ * ITCs. Until that time we have to avoid ITC.
+ */
+ clocksource_itc.rating = 50;
/* Setup the CPU local timer tick */
ia64_cpu_local_tick();