They determine the initialization order of built-in modules. Drivers will use device_initcall (or module_init; see below) most of the time. Early initialization (early_initcall) is normally used by architecture-specific code to initialize hardware subsystems (power management, DMAs, etc.) before any real driver gets initialized. Technical stuff for understanding below Look at init/main.c. After a few architecture-specific … Read more
Linux Kernel Newbies, imho, is the best resource for who wants to start in linux kernel development. Maybe you are interested to buy a book: Linux Kernel Development 3rd edition 2010; Understanding the linux kernel 3rd edition 2005; Linux Device Drivers 3rd edition 2005. Free resources (only a few of them): Linux Kernel Hacking; Hacking … Read more
What is your kernel? Is it from the linux distributive you use or is it compiled by you (how did you install it)? First part of warning says about /proc/kallsyms – can you show output of the command (started from the same user you used to run perf) ls -l /proc/kallsyms cat /proc/kallsyms | head … Read more
spin_lock_irqsave is basically used to save the interrupt state before taking the spin lock, this is because spin lock disables the interrupt, when the lock is taken in interrupt context, and re-enables it when while unlocking. The interrupt state is saved so that it should reinstate the interrupts again. Example: Lets say interrupt x was … Read more
This is an optimization done by linux/glibc to make futexes faster when they’re not shared between processes. Glibc will use the _PRIVATE versions of each of the futex calls unless the PTHREAD_PROCESS_SHARED attribute is set on your mutex It’s explained in more detail here: http://lwn.net/Articles/229668/ For the purposes of your debugging, you can just ignore … Read more
My answer is true for Intel CPUs running on a modern Linux system, and I am speaking about user-level processes, not kernel code. Still, I think it’ll give you some insight enough to think about the other possibilities Address Types Regarding question 3: I have come across discussion that virtual and logical addresses/address space are … Read more
Long story short: the probe() function of the driver is called as a result of calling the register_driver for that specific bus. More precisely, it’s called by the probe() of that bus_type structure. In your case: i2c_bus_type. Here’s the call chain in your I2C case: i2c_register_driver driver_register bus_add_driver driver_attach __driver_attach (for your device) driver_probe_device really_probe … Read more
1) By default, perf stat shows task-clock, and does not show cpu-clock. Therefore we can tell task-clock was expected to be much more useful. 2) cpu-clock was simply broken, and has not been fixed for many years. It is best to ignore it. It was intended that cpu-clock of sleep 1 would show about 1 … Read more
I assume, this refers to the same as the (y,n,m) prompt when running make config; in that case it would be “module”. Note that compiling Unix domain sockets (CONFIG_UNIX) as module is probably not a good idea. A lot of system components and programs depend on them, and some services might fail to start up … Read more
I had the same problem with Debian 8. I fixed it by restarting the system. It seems that the error can occur if the kernel image was updated and the system was not restarted thereafter.