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Subject: Re: [PATCH v5 1/2] sched/clock: interface to allow timestamps early
 in boot
To: Thomas Gleixner <tglx@linutronix.de>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org, mingo@redhat.com,
        peterz@infradead.org, hpa@zytor.com, douly.fnst@cn.fujitsu.com
References: <1503520884-99253-1-git-send-email-pasha.tatashin@oracle.com>
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 <alpine.DEB.2.20.1708260018160.2124@nanos>
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 <alpine.DEB.2.20.1708281701590.1867@nanos>
From: Pasha Tatashin <pasha.tatashin@oracle.com>
Message-ID: <a0487461-3344-6a5d-281e-087e13f0c60b@oracle.com>
Date: Mon, 28 Aug 2017 13:59:29 -0400
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>> 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.
> 

OK, how about reading the persistent clock only once, and send it's 
value to use for calculation of boot stamp to read_boot_clock64() via a 
new argument:

read_boot_clock64(&now, &boot);

Does this sound alright or is there a better way?

I would need to update read_boot_clock64() everywhere it is declared to 
add the __init macro, so this extra argument is not going to increase 
number of line changes.

Thank you,
Pasha