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    SubjectRe: [RFC 1/2] printk: Enable platform to provide a early boot clock
    On Thu, 14 Jun 2018, Feng Tang wrote:
    > On Wed, May 30, 2018 at 05:20:58PM +0800, Feng Tang wrote:
    > > Currently printk timestamp mostly come from the sched_clock which
    > > depends on the clock setup, so there are many kernel logs started
    > > with "[ 0.000000] " before the clock is calibrated.
    > >
    > > This patch will provide an debug option for specific platform to
    > > provide a early boot time clock, so that we can have time info in
    > > kernel log much earlier, which can show the time info for the early
    > > kernel boot, and make boottime tuning/optimization easier (boot time
    > > is critical for phone/tablet and embedded devices).
    > >
    > > Capable platform only need to setup the "boot_printk_clock_fn"
    > > which could return time in nano seconds.
    > >
    > > Together with a TSC patch on x86 system, we have easily captured
    > > some early boottime killer like unwind_init() which takes about
    > > 300ms in boot phase.
    >
    > Hi Petr and all,
    >
    > As the 2/2 tsc related patch is still under review/discussion, can
    > we consider taking this first? As this may benefit other archs.
    > For example, Intel Curie platform has an always-on 32KHz osc clock,
    > which is accurate but low frequency, and it could be used as
    > early printk timestamp until the high-resolution timer is initialized
    > and used as sched_clock. Don't know if ARM or other platforms
    > have similar use case.

    Can we please _NOT_ add half sorted core stuff in a hurry?

    Thanks,

    tglx

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