Debugging Linux Kernel using ftrace Part13 - Finding out maximum time interrupts are disabled

-
When interrupts are disabled, CPU cannot react to any external events:
  • timer interrupts
  • mouse interrupts

irqsoff is a tracer which tracks the times in the kernel when interrupts are disabled. Whenever a new maximum latency is found, the tracer saves the trace leading up to that latency point. Each time a new maximum latency is reached, the old saved trace is discarded and the new trace is saved.

By default this tracer is not enabled in my kernel, I had to re-compile my linux kernel with the following kernel configuration: "CONFIG_IRQSOFF_TRACER"


You can see from the above screenshot, the maximum latency found was 644ms, started at _raw_spin_lock_irq.  Also , 'tracing_max_latency' file also provides you the maximum latency when the interrupts are disabled.

Next time, trace file will be updated when it finds a latency greater than the value present in 'tracing_max_latency' file.

To reset the maximum latency, write '0' in 'tracing_max_latency' file.
echo 0 > tracing_max_latency

Comments

Post a Comment

Popular posts from this blog

bb.utils.contains yocto

-
Image
bb.utils.contains  is most commonly used function in Yocto. grep in poky directory returned with 696 count. $ grep -nr 'bb.utils.contains' poky/ | wc -l 696 It's definition is present in 'poky/bitbake/lib/bb/utils.py' file This function returns third argument if the second argument is subset of the first argument else returns fourth argument Let's take an example to understand this. You can see from the above screenshot, when the second argument is a subset of first argument, "present" was returned, else "notpresent" was returned We can also use bb.utils.contains inside if loop. This we can use inside a recipe. if ${@bb.utils.contains('SOMEFLAG','NEWVALUE3','true','false',d)}; then     FOO = 'HELLO' fi
Read more

make config vs oldconfig vs defconfig vs menuconfig vs savedefconfig

-
Image
Building the Linux Kernel is a two-step process: Configuring the Kernel options Building the Kernel with those options. There are many methods available for configuring the kernel. make config: Text-based Configuration.  Options are prompted one after another. All options need to be answered Access to former options is not possible make menuconfig: Menu-driven user interface Allows to navigate forwards and backward directly between features Allows to load and save files with filenames different from ".config" Provides search feature It uses ncurses library for GUI. If the ncurses library is not installed, make menuconfig option fails. To install ncurses library on Ubuntu: sudo apt-get install libncurses5-dev make defconfig: Creates a ".config" file with default options from the ARCH supplied defconfig Configurations are generally stored in the directory: arch/$(ARCH)/configs $ ls arch/x86/configs/ i386_defconfi
Read more

PR, PN and PV Variable in Yocto

-
PN : Represents the name of the recipe. The name is usually extracted from the recipe file name. PR:  Represents the revision of the recipe. Default value for this revision is "r0". Subsequent revisions of the recipe conventionally will have "r1", "r2" and so on. PV:  Represents the version of the recipe. Normally extracted from the recipe file name. For example: ffmpeg_3.4.2.bb recipe. ${PN} : ffmpeg ${PV} : 3.4.2
Read more