Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early in boot

[Peter Zijlstra]

On Wed, Sep 27, 2017 at 03:45:06PM +0100, Russell King - ARM Linux wrote:
> On Wed, Aug 30, 2017 at 02:03:22PM -0400, Pavel Tatashin wrote:
> > In Linux printk() can output timestamps next to every line.  This is very
> > useful for tracking regressions, and finding places that can be optimized.
> > However, the timestamps are available only later in boot. On smaller
> > machines it is insignificant amount of time, but on larger it can be many
> > seconds or even minutes into the boot process.
> 
> The sched_clock work I did for ARM could be setup really early at boot,
> from setup_arch().  I tried to encourage platforms to do that, but all
> my encouragement fell on deaf ears - most people setup the sched_clock
> source along side the time initialisation on ARM.
> 
> I don't think we need yet another "early" mechanism to solve this problem,
> we just need people to use the existing mechanism to register their
> sched_clock implementation earlier.

x86 is a bit 'special' in the whole sched_clock department. But yes, we
should very much make the regular sched_clock() happen earlier.