linux-kernel - Re: [PATCH] printk: Add printk_flush() to force buffered text to console

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Date:	Mon, 25 Jun 2012 09:53:28 -0700
From:	Joe Perches <joe@...ches.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"kay.sievers" <kay.sievers@...y.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] printk: Add printk_flush() to force buffered text to
 console

On Mon, 2012-06-25 at 10:45 +0200, Ingo Molnar wrote:
> * Joe Perches <joe@...ches.com> wrote:
> 
> > On Sat, 2012-06-23 at 08:13 +0200, Ingo Molnar wrote:
> > > * Andrew Morton <akpm@...ux-foundation.org> wrote:
> > > 
> > > > On Thu, 21 Jun 2012 19:52:03 -0400
> > > > Steven Rostedt <rostedt@...dmis.org> wrote:
> > > > 
> > > > > But with the new printk() changes, text without a newline 
> > > > > gets buffered and does not print out to the console at the 
> > > > > location of the printk.
> > > > 
> > > > uh, how about we fix that?  The old behaviour was good, the 
> > > > new behaviour is noxious.
> > > 
> > > Absolutely.
> > > 
> > > pr_flush() really seems to be a workaround.
> > 
> > I think the new behavior an overall improvement.
> > It helps avoid multiple thread interleaving.
> > 
> > I suggested a fix to enable a printk buffered/non-buffered
> > mechanism with an optional printk_flush/pr_flush.
> > 
> > https://lkml.org/lkml/2012/6/21/305
> 
> Ugh, so you suggest a global toggle to turn buffering on/off?

<shrug>

Rather than adding a bunch of printk_flush() calls around
the possibly many sites per file that need them, I'd rather
see a code block surrounded by buffer(false)/buffer(true).

I'd actually rather see the existing partial line uses like:

	printk("doing test_func: ");
	printk("%s\n", test_func(foo) ? "successful", "failed");

and

	printk("step 1")
	bar();
	printk(" - step 2");
	baz();
	printk("completed\n");
		
changed to whole lines rather than adding a bunch of
printk_flush() sites or the printk_buffering(on|off)
blocks.

Anyway, I suggested it shouldn't be merged awhile ago.

https://lkml.org/lkml/2012/5/22/439

Making systemic printk changes is a slow business.


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