linux-kernel - Re: [PATCH] arm64: Neaten show_regs, remove KERN

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Date:   Mon, 24 Oct 2016 17:42:55 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Joe Perches <joe@...ches.com>
Cc:     linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm64: Neaten show_regs, remove KERN_CONT

On Mon, Oct 24, 2016 at 09:27:57AM -0700, Joe Perches wrote:
> On Mon, 2016-10-24 at 12:31 +0100, Mark Rutland wrote:
> > On Sun, Oct 23, 2016 at 01:40:49PM -0700, Joe Perches wrote:
> > > commit db4b0710fae9 ("arm64: fix show_regs fallout from KERN_CONT changes")
> > > corrected the KERN_CONT fallout from commit 4bcc595ccd80
> > > ("printk: reinstate KERN_CONT for printing continuation lines"), but
> > > the code still has unnecessary KERN_CONT uses.  Remove them.
> > 
> > Why are these unnecessary KERN_CONTs a larger problem than duplicating
> > the format string for a third time? Having to duplicate it at all was
> > annoying enough.
> 
> Not printing partial lines is the best solution to avoiding
> message output interleaving.

Would you mind mentioning that explicitly in the commit message? That
makes it obvious what the benefit of avoiding KERN_CONT is.

> > Overall, to avoid messing with the KERN_CONT mess it'd be nicer to
> > format this all into a buffer (with the format string only existing the
> > once) and subsequently print it with one printk call
> 
> A single printk call would get one timestamp which would
> make for ragged/staggered reading.

That does not appear to be the case; as fr as I can tell the core prints a
timestamp per line as required. If I run:

	printk("TEST\nLINE1\nLINE2\nLINE3\nLINE4\n");

... with "printk.time=1", over the UART:

	[   41.201864] TEST
	[   41.201864] LINE1
	[   41.201864] LINE2
	[   41.201864] LINE3
	[   41.201864] LINE4

... with "printk.time=1", via the $(dmesg):

	[   41.201864] TEST
	[   41.201864] LINE1
	[   41.201864] LINE2
	[   41.201864] LINE3
	[   41.201864] LINE4

... with "printk.time=0", over the UART:

	TEST
	LINE1
	LINE2
	LINE3
	LINE4

... with "printk.time=0", via the $(dmesg):

	TEST
	LINE1
	LINE2
	LINE3
	LINE4

... with "printk.time=0", via $(dmesg -T):

	[Mon Oct 24 17:38:37 2016] TEST
	[Mon Oct 24 17:38:37 2016] LINE1
	[Mon Oct 24 17:38:37 2016] LINE2
	[Mon Oct 24 17:38:37 2016] LINE3
	[Mon Oct 24 17:38:37 2016] LINE4

Thanks,
Mark.