linux-kernel - Re: [tip:sched/urgent] sched: Restore printk sanity

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Date:	Sun, 27 Dec 2009 06:56:37 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Valdis.Kletnieks@...edu
Cc:	Pavel Machek <pavel@....cz>, mingo@...hat.com, hpa@...or.com,
	linux-kernel@...r.kernel.org, joe@...ches.com,
	torvalds@...ux-foundation.org, peterz@...radead.org, efault@....de,
	akpm@...ux-foundation.org, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org,
	Alexander Viro <viro@....linux.org.uk>
Subject: Re: [tip:sched/urgent] sched: Restore printk sanity


* Valdis.Kletnieks@...edu <Valdis.Kletnieks@...edu> wrote:

> On Fri, 25 Dec 2009 19:45:14 +0100, Ingo Molnar said:
> 
> >  - in the last stable kernel, v2.6.32, still more new printk()s were 
> >    introduced than pr_*() lines:
> > 
> >      $ git log -p v2.6.31..v2.6.32 | grep '^+.*\<pr_' | wc -l
> >      2016
> >      $ git log -p v2.6.31..v2.6.32 | grep '^+.*\<printk' | wc -l
> >      3531
> 
> Ahem. That's not introduced, that's 'added or modified'.

'introduced or modified', yes. In those 5500 lines less than ~20% are 
'modifications' (the rest is newly introduced).

> % git log -p v2.6.31..v2.6.32 | grep -C 5 '^+.*\<pr_' | head
> -        * In case of failure continue with no timer. */
> +       /* Test if the external timer can be actually used.
> +        * In case of failure continue without timer. */
>         if (unlikely((stmmac_open_ext_timer(dev, priv->tm)) < 0)) {
> -               pr_warning("stmmaceth: cannot attach the HW timer\n");
> +               pr_warning("stmmaceth: cannot attach the external timer.\n");
>                 tmrate = 0;
>                 priv->tm->freq = 0;
>                 priv->tm->timer_start = stmmac_no_timer_started;
>                 priv->tm->timer_stop = stmmac_no_timer_stopped;
> 
> Meanwhile, the fact that there's only about a 2-to-1 difference in patches 
> when there's a 6-to-1 difference in existing code tells me that 
> proportionally, there is *more* activity with pr_foo variants than printk.

Yet there's more printks in the kernel than a cycle ago, so without the trend 
changing, we've got an infinite supply of future 'conversion' patches.

> printk:  3531 hits in 61126 uses = 5.7% churn
> pr_foo: 2016 hits in 10861 uses = 18.5% churn

Peter's complaint was precisely that there's a lot of 'churn' for pr_*().

> The numbers need much deeper analysis to make any sort of real statistical 
> conclusion here...

If you are convinced that there's something else going on as well feel free to 
do deeper analysis. So, until some contrary numbers are posted i stay by my 
main conclusions.

Thanks,

	Ingo
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