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

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Message-ID: <20120615120430.GB23681@gmail.com>
Date:	Fri, 15 Jun 2012 14:04:30 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Fengguang Wu <fengguang.wu@...el.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"kay.sievers" <kay.sievers@...y.org>,
	"Paul E. McKenney" <paulmck@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] printk: Add printk_flush() to force buffered text to
 console


* Greg Kroah-Hartman <gregkh@...uxfoundation.org> wrote:

> On Fri, Jun 15, 2012 at 12:22:33PM +0800, Fengguang Wu wrote:
> > > I actually would like to make these more compact. As all my test box
> > > consoles go through serial ports, just booting through this takes more
> > > time the the compile itself.
> > 
> > The tests took 23 seconds boot time on one kernel:
> > 
> >         [    0.152934] Testing tracer nop: PASSED
> >         ...1577 lines total...
> >         [   23.206550] Testing kprobe tracing: OK
> > 
> > And 135 seconds in another bloated kernel:
> > 
> >         [  115.396441] Testing event 9p_client_req: OK
> >         ...2545 lines total...
> >         [  240.268783] Testing kprobe tracing: OK
> > 
> > I'd appreciate if the boot time can be reduced. Because I'm doing
> > kernel boot tests for *every single* commits.
> > 
> > It may look insane amount of work, but it's still manageable: with 10
> > kvm instances each take 1 minute to boot test a kernel, I can boot
> > test 60*24*10=14400 kernels in one day. That's a rather big number.
> > That allows me to run more cpu/vm/io stress tests for each kernel :-)
> 
> Do you really want to enable those tests for your test 
> kernels?  Can they fail if we mess up other parts of the 
> kernel, or do they only test the tracing portions?

These printk's are useful, are used for a specific (albeit 
limited) purpose and were and continue to be useful in that 
role.

The changes Steve bisected to broke this use of printk(). Please 
apply Steve's fix, fix it yourself or revert the changes that 
regressed printk().

Thanks,

	Ingo
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