Saturday, 31 December 2016

Kernel printk statements

The kernel contains tens of thousands of statements that may print various errors, warnings and debug/information messages to the kernel log.  Unsurprisingly, as the kernel grows in size, so does the quantity of these messages.  I've been scraping the kernel source for various kernel printk style statements and macros and scanning these for various typos and spelling mistakes and to make this easier I hacked up kernelscan (a quick and dirty parser) that helps me find literal strings from the kernel for spell checking.

Using kernelscan, I've gathered some statistics for the number of kernel print statements for various kernel releases:

As one can see, we have over 200,000 messages in the 4.9 kernel(!).  Given the kernel growth, we can see this seems to roughly correlate with the kernel source size:

So how many lines of code in the kernel do we have per kernel printk messages over time?

..showing that the trend is to have more lines of code per frequent printk statements over time.  I didn't differentiate between different types of printk message, so it is hard to see any deeper trends on what kinds of messages are being logged more or less frequently over each release, for example,  perhaps there are less debug messages landing in the kernel nowadays.

I find it quite amazing that the kernel contains quite so many printk messages; it would be useful to see just how many of these are actually in a production kernel. I suspect quite large number are for driver debugging and may be conditionally omitted at build time.

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