Re: [Announce] Linux-tiny project revival

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To: Rob Landley <rob@...>
Cc: Indan Zupancic <indan@...>, <linux-tiny@...>, Michael Opdenacker <michael@...>, CE Linux Developers List <celinux-dev@...>, linux kernel <linux-kernel@...>
Date: Friday, September 21, 2007 - 5:34 pm

On Sep 20, 2007, at 19:18:41, Rob Landley wrote:

That's actually a fairly straightforward problem to solve.  Really we  
ought to be able to guarantee that lines from different CPUs are not  
intermixed.  This can end up in a log like this:

info: Current device state: <1>netdev watchdog timeout: eth0
reg1=0xABCD reg2=0xDEADBEEF

Clearly unpleasant, no?  Really any logging which wants to print out  
a bunch of stuff with multiple printk()s should use an API something  
like this:

Option 1: Buffer allocated with kmalloc().  Sleep-ish context, can  
handle failures easily


Option 2: Preallocated per-cpu buffer.  preempt_disable()d


Option 3: Preallocated per-cpu interrupts-only buffer.  Only from  
code which may interrupt a preempt_disable() section


For all of the above, the final "qprintk_finish()" call would  
essentially take the printk spinlock and write the contents of the  
qpk->buffer into the dmesg ringbuffer, inserting ("<%d>", level) at  
the beginning and after each newline.  The buffers would all be some  
useful fixed size (a page?); if you need more than that then you are  
probably trying to queue too much and excess data would be truncated.

Since the level would be a constant passed to qprintk_ 
{kmalloc,percpu,irq} in almost every case, you could easily do  
something like this:

static inline int qprintk_kmalloc(struct printk_queue *qpk,
		unsigned int level, gfp_t gfp)
{
	if (level > CONFIG_MAX_LOG_LEVEL) {
		qpk->type = QPRINTK_TYPE_NONE; /* also 0 */
		qpk->buffer = NULL;
		return 0;
	}

	_qprintk_kmalloc(qpk, level, gfp);
}

#define qprintk(QPK, FMT...) do { \
		if ((QPK)->type)
			_qprintk(QPK, FMT);
	} while(0)


With a bit more glue that would cause GCC to notice that for a given  
qprintk_kmalloc the "qpk->type" is always zero because the level is  
too high, and therefore it would optimize out *ALL* of the  
_qprintk_kmalloc(), _qprintk(), and _qprintk_finish() calls.

Cheers,
Kyle Moffett

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Messages in current thread:
[Announce] Linux-tiny project revival, Tim Bird, (Wed Sep 19, 2:03 pm)
Re: [Announce] Linux-tiny project revival, Rob Landley, (Thu Sep 20, 4:38 pm)
Re: [Announce] Linux-tiny project revival, Arnd Bergmann, (Thu Sep 27, 3:00 am)
Re: [Announce] Linux-tiny project revival, Rob Landley, (Thu Sep 27, 8:06 pm)
Re: [Announce] Linux-tiny project revival, Indan Zupancic, (Thu Sep 27, 12:35 pm)
Re: [Announce] Linux-tiny project revival, Arnd Bergmann, (Thu Sep 27, 6:21 pm)
Re: [Announce] Linux-tiny project revival, Bernd Petrovitsch, (Fri Sep 28, 4:39 am)
Re: [Announce] Linux-tiny project revival, Jörn, (Sun Sep 30, 4:37 pm)
Re: [Announce] Linux-tiny project revival, Bill Davidsen, (Fri Sep 21, 8:27 am)
Re: [Announce] Linux-tiny project revival, Tim Bird, (Thu Sep 20, 5:58 pm)
Re: [Announce] Linux-tiny project revival, Joe Perches, (Thu Sep 20, 6:14 pm)
Re: [Announce] Linux-tiny project revival, Rob Landley, (Thu Sep 20, 8:28 pm)
Re: [Announce] Linux-tiny project revival, Joe Perches, (Thu Sep 20, 8:03 pm)
Re: [Announce] Linux-tiny project revival, Rob Landley, (Thu Sep 20, 7:11 pm)
Re: [Announce] Linux-tiny project revival, Indan Zupancic, (Thu Sep 20, 5:26 pm)
Re: [Announce] Linux-tiny project revival, Rob Landley, (Thu Sep 20, 7:18 pm)
Re: [Announce] Linux-tiny project revival, Kyle Moffett, (Fri Sep 21, 5:34 pm)
Re: [Announce] Linux-tiny project revival, Joe Perches, (Fri Sep 21, 6:05 pm)
Re: [Announce] Linux-tiny project revival, Kyle Moffett, (Fri Sep 21, 6:57 pm)
Re: [Announce] Linux-tiny project revival, Joe Perches, (Fri Sep 21, 1:45 pm)
Re: [Announce] Linux-tiny project revival, Rob Landley, (Fri Sep 21, 7:05 pm)
Re: [Announce] Linux-tiny project revival, Joe Perches, (Fri Sep 21, 7:08 pm)
Re: [Announce] Linux-tiny project revival, Indan Zupancic, (Thu Sep 20, 7:06 pm)
Re: [Announce] Linux-tiny project revival, Sam Ravnborg, (Fri Sep 21, 2:29 am)
Re: [Announce] Linux-tiny project revival, Adrian Bunk, (Mon Sep 24, 2:13 pm)
Re: [Announce] Linux-tiny project revival, Rob Landley, (Wed Sep 26, 2:24 am)
Re: [Announce] Linux-tiny project revival, Joe Perches, (Thu Sep 20, 4:16 pm)
Re: [Celinux-dev] Re: [Announce] Linux-tiny project revival, Geert Uytterhoeven, (Tue Sep 25, 7:43 am)
Re: [Announce] Linux-tiny project revival, Alexey Dobriyan, (Thu Sep 20, 3:58 pm)
Re: [Announce] Linux-tiny project revival, Rob Landley, (Thu Sep 20, 6:02 pm)
Re: [Announce] Linux-tiny project revival, Jared Hulbert, (Thu Sep 20, 5:22 pm)
Re: [Announce] Linux-tiny project revival, Rob Landley, (Thu Sep 20, 6:53 pm)
Re: printk proposal - (was Linux-tiny project revival), Alexey Dobriyan, (Fri Sep 21, 3:07 pm)
Re: printk proposal - (was Linux-tiny project revival), Rob Landley, (Fri Sep 21, 4:53 pm)
Re: [Celinux-dev] [Announce] Linux-tiny project revival, Andrew Morton, (Wed Sep 19, 5:28 pm)
Re: [Celinux-dev] [Announce] Linux-tiny project revival, Michael Opdenacker, (Wed Sep 19, 6:38 pm)
Re: [Celinux-dev] [Announce] Linux-tiny project revival, Andy Whitcroft, (Thu Sep 20, 5:10 am)
Re: Monster switch for small size (was Linux-tiny revival), Christian MICHON, (Fri Sep 21, 2:35 am)
Re: [Announce] Linux-tiny project revival, Andi Kleen, (Wed Sep 19, 3:28 pm)
Re: [Announce] Linux-tiny project revival, Tim Bird, (Wed Sep 19, 3:41 pm)
Re: [Announce] Linux-tiny project revival, Tim Bird, (Wed Sep 19, 5:29 pm)
Re: [Announce] Linux-tiny project revival, Michael Opdenacker, (Wed Sep 19, 6:29 pm)
Re: [Announce] Linux-tiny project revival, Christian MICHON, (Wed Sep 19, 3:01 pm)
Re: [Announce] Linux-tiny project revival, Luis R. Rodriguez, (Wed Sep 19, 2:47 pm)
Re: [Announce] Linux-tiny project revival, Tim Bird, (Wed Sep 19, 3:31 pm)