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    SubjectRe: CONFIG_PRINTK_TIME woes
    * Andrew Morton <akpm@osdl.org> [050821 02:15]:
    > "Luck, Tony" <tony.luck@intel.com> wrote:
    > >
    > > 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.

    CONFIG_PRINTK_TIME also has a problem on at least ARM OMAP where
    the IO mapping to read the clock may not be initialized when
    sched_clock() is called for the first time.

    I'd hate to have to test for something for CONFIG_PRINTK_TIME
    every time sched_clock() is being called.

    The quick fix would seem to be to only allow CONFIG_PRINTK_TIME
    from kernel cmdline to make it happen a bit later. So basically
    make int printk_time = 0 until command line is evaluated.

    Tony
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