[$] Improving printk()

When a kernel developer wants to communicate a message to user space, be itfor debugging or to report a serious problem with the system, the venerableprintk() function is usually the tool of choice. But, as SteveRostedt (accompanied by Petr Mladek and Sergey Senozhatsky) noted during abrief session at the 2017 Kernel Summit, printk() has not aged well. In particular, it can affect theperformance of the system as a whole; the roots of that problem and apossible solution were discussed, but a real solution will have to wait forthe appearance of the code.