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. Thanks, Feng