It has been pointed out to me that ia64 doesn't boot with CONFIG_PRINTK_TIME=y. The issue is the call to sched_clock() ... which on ia64 accesses some per-cpu data to adjust for possible variations in processor speed between different cpus. Since the per-cpu page is not set up for the first few printk() calls, we die.
Is this an issue on any other architecture? Most versions of sched_clock() seem to just scale jiffies into nanoseconds, so I guess they don't. s390, sparc64, x86 and x86_64 all have more sophisticated versions but they don't appear to me to have limitations on how early they might be called. Possible solutions: 1) Fix ia64 version of sched_clock() to check whether the per-cpu page hase been initialized before using it. I don't like this solution as it will make sched_clock() slower for its primary uses in kernel/sched.c ... none of which can be called before the per-cpu area is initialized. 2) Add some test to the printk() path along the lines of: t = (can_call_sched_clock) ? sched_clock() : 0; This is somewhat ugly ... perhaps too unpleasant for words in that can_call_sched_clock is a per-cpu concept! 3) Make the printk() code get the time in some other way. Using sched_clock() here seems wrong. The ia64 version has a big fat comment about not comparing the results of two calls from different cpus ... but since printk() calls can come from any cpu ... it seems likely that a user who turns on PRINTK_TIME might subtract timestamps from two lines to see how long it was between the messages. This could have significant error on a system that has been up for a long time. But I don't have a better suggestion from existing code. I assume that sched_clock() was picked as it is both fast and lockless. -Tony - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
