On Wed, 28 May 2014 19:22:39 +0200 Peter Zijlstra <pet...@infradead.org> wrote:
> On Wed, May 28, 2014 at 01:14:40PM -0400, Steven Rostedt wrote: > > > > trace_printk() is used to debug fast paths within the kernel. Places > > that gets called in any context (interrupt or NMI) or thousands of > > times a second. Something you do not want to do with a printk(). > > > > In order to make it completely lockless as it needs a temporary buffer > > to handle some of the string formatting, a page is created per cpu for > > every context (four per cpu; normal, softirq, irq, NMI). > > > > Since trace_printk() should only be used for debugging purposes, > > there's no reason to waste memory on these buffers on a production > > system. That means, trace_printk() should never be used unless a > > developer is debugging their kernel. There's macro magic to allocate > > the buffers if trace_printk() is used anywhere in the kernel. > > > > To help enforce that trace_printk() isn't used outside of development, > > when it is used, a nasty banner is displayed on bootup (or when a module > > is loaded that uses trace_printk() and the kernel core does not). > > > > Here's the banner: > > > > **************************************** > > ** NOTICE NOTICE NOTICE NOTICE NOTICE ** > > ** trace_printk() being used. ** > > ** Allocating extra memory for it ** > > **************************************** > > > > Hmm, maybe I should add "Not for production use" to scare people even > > more? > > Does that really stop people from doing stupid? Wouldn't it be better to Scary banners usually do. Perhaps this isn't scary enough. > make sure nobody merges a trace_printk() user in mainline? You can set > up a commit hook and check for +.*trace_printk or so. Of course, but that requires me to monitory it. It may be too late when I notice it. Nothing prevents me from doing both :-) -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
