linux-kernel - Re: [PATCH v5 1/2] sched/clock: interface to allow timestamps early in boot

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Date:   Mon, 28 Aug 2017 17:13:58 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Pasha Tatashin <pasha.tatashin@...cle.com>
cc:     x86@...nel.org, linux-kernel@...r.kernel.org, mingo@...hat.com,
        peterz@...radead.org, hpa@...or.com, douly.fnst@...fujitsu.com
Subject: Re: [PATCH v5 1/2] sched/clock: interface to allow timestamps early
 in boot

On Mon, 28 Aug 2017, Pasha Tatashin wrote:
> This makes sense. Changing order in timekeeping_init(void) should take care of
> this:
> 
> Change to:
> 
> void __init timekeeping_init(void)
> {
> 	/*
> 	 * We must determine boot timestamp before getting current  	
> 	 * persistent clock value, because implementation of
> 	 * read_boot_clock64() might also call the persistent
> 	 * clock, and a leap second may occur.
> 	 */
> 
> 	read_boot_clock64(&boot);
> 	...
> 	read_persistent_clock64(&now);

No. That's the same crap just the other way round.

s390 can do that, because the boot timestamp is correlated with the
persistent clock. Your's not so much.

Thanks,

	tglx