In a system running kernel version 2.6.38 I see this sysfs file which shows the current clock source (happens to be tsc) /sys/devices/system/clocksource/clocksource0/current_clocksource
But looks like this sysfs file was introduced recently. In 2.6.9 I don't see this file. In versions that doesn't have this sysfs is there an easy to see the clock source ? When I compare the clock_gettime() ouptputs in these versions 2.6.9 seems to be at microseconds granularity and 2.6.38 is at nanoseconds granularity. Hence wondering what the clock source in 2.6.9 is..
You could try grepping clocksource and TSC from dmesg output.
FWIW, the high-resolution timers (which enabled nanosecond resolution, among many other things) were introduced in the 2.6.21 kernel or thereabouts; older kernels don't have that, as you have found out.
Related
In Yocto project, built my project which is running on Raspbian OS. When i run executable, i get half FPS compared to executable running on Raspbian OS.
The libraries i use:
OpenCV
Tensorflow-Lite, Flatbuffer, Libedgetpu
I use Libedgetpu1-std, Tensorflow-lite 2.4.0 on Raspbian and Libedgetpu 2.5.0, Tensorflow-lite 2.5.0 on Yocto.
Thinking that the problem is that the versions or configurations of the libraries are not the same, i followed these steps:
I ran the executable which i built in Raspbian directly in the runtime of the Yocto project.(I have set the required library versions to the same library versions available in raspbian for it to work in runtime.)
But i still got low FPS. Here is how i calculate that i get half the FPS:
I am using TFLite's interpreter invoke function. I set a timer when entering and exiting the function, i calculate FPS over it. I can exemplify like this:
Timer_Begin();
m_tf_interpreter->Invoke();
Timer_End();
Somehow i think the Interpreter Invoke function is running slower on the Yocto side. I checked Kernel versions, CPU speeds, /boot/config.txt contents, USB power consumes of Raspbian and Yocto. However, I couldn't catch anything from anywhere.
Note : Using RPI4 and Coral-TPU(Plugged into USB 2.0).
We spoke with #Paulo Neves. He recommend Perf profiling and i did . In the perf profiling, i noticed that the CPU is running slowly. Although the frequencies are the same.
When i check the "scaling_governor", i saw that it was in "powersave" mode. The problem solved when i switched from "powersave" to "performance" mode from virtual kernel.
In addition, if you want to make the governor change permanent, you need to create a kernel config fragment.
I need to count the transitions of a 50KHz binary signal using a BBB. I think using the TIMER4 triggered by the external signal connected to the pin P8.07 would be the easiest way.
So, I issued the following commands to load the proper cape and setup the pin as a timer :
./config-pin overlay cape-universaln
./config-pin P8.07 timer
Everything seems to work and nothing appears in dmesg.
My question is : How can I read the value of TIMER4 ? I looked in SysFs and find nothing interesting. Nothing in /dev as well. How can I retrieve the value of the timer counter I just setup ? I'm open to a C/C++ solution as well, but I would like to avoid doing kernel-space programming.
I'm using the latest Ubuntu Linux for BeagleBone, kernel 4.1.10-ti-r21.
With a little googling I see a pps driver for the AM335x DMTimer subsystem here: https://github.com/ddrown/pps-gmtimer
It looks like it hasn't been merged upstream and the README gives instructions on building it into the 3.8 kernel - you could revert back to 3.8, or you could adapt that for 4.1, in which case you may need to tweak the Device Tree overlay as well for the newer version of the dtc compiler that's in 4.1.
You could also write a pulse counter firmware for the PRU (with only a 50KHz input it wouldn't need to be very optimized at all to catch every pulse). You could send a signal to the ARM every so often and catch that in your userspace program.
Another option would be to directly access the DMTimer registers from userspace using mmap to map the /dev/mem file (example of this method for GPIO here), but that's a pretty "hacky" way to do it, and it's generally frowned upon in the GNU/Linux world to do that sort of stuff from userspace instead of from kernal space.
Is it possible to upgrade only a specific sub-system, say I2C, of the Linux Kernel.
For example:
Is it possible to include "Support for multiplexed I2C bus topologies (introduced in Kernel 2.6.36)" in the Kernel version 2.6.31.1.
No this is not possible.
A kernel module or 'subsystem' (eg the i2c module) is build for a specific kernel image, you cannot combine different kernel(module) versions.
If you are feeling lucky (depending on your kernel skills), you could:
download the source code of your kernel
Install compiler and friends
add the updated ic2 driver
Try to compile the module for your kernel version
Cross your fingers and load it into your own kernel...\
I do not have any experience with this, so I do not know whether this works or not. Of course, if the ic2 module requires other (updated) modules, you could be ending up with updating (almost) the complete kernel...
I have a question about changing kernel frequency.
I compiled kernel by using:
make menuconfig(do some changes in config)
(under Processor type and features->Timer frequency to change frequency)
1.fakeroot make-kpkg --initrd --append-to-version=-mm kernel-image kernel-headers
2.export CONCURRENCY_LEVEL=3
3.sudo dpkg -i linux-image-3.2.14-mm_3.2.14-mm-10.00.Custom_amd64.deb
4.sudo dpkg -i linux-headers-3.2.14-mm_3.2.14-mm-10.00.Custom_amd64.deb
then say if I want to change the frequency of kernel,
what I did is:
I replaced .config file with my own config file
(since I want to do this automatically without opening make menuconfig ui)
then I repeat the step1,2,3,4 again
Is there anyway I do not need repeat the above 4 steps?
Thanks a lot!!!!
The timer frequency is fixed in Linux (unless you build a tickless kernel - CONFIG_NO_HZ=y - but the upper limit will still be fixed). You cannot change it at runtime or at boot time. You can only change it at compile time.
So the answer is: no. You need to rebuild the kernel when you want to change it.
The kernel timer frequency (CONFIG_HZ) is not configurable at runtime - you will have to compile a new kernel when you change the setting and you will have to reboot the system with the new kernel to see the effects of any change.
If you are doing this a lot, though, you should be able to create a little shell script to automate the kernel configure/build/install process. For example it should not be too hard to automate the procedure so that e.g.
./kernel-prep-with-hz 100
would rebuild and install a new kernel, only requiring from you to issue the final reboot command.
Keep in mind though, that the timer frequency may subtly affect various subsystems in unpredictable ways, although things have become a lot better since the tickless timer code was introduced.
Why do you want to do this anyway?
Maybe this will help. As the articale says, you can change the frequency between the available frequency that your system supports. (Check if CPUfreq is already enabled in your system)
Example, mine.
#cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
2000000 1667000 1333000 1000000
#echo 1000000 > cpu0/cpufreq/scaling_min_freq
http://www.ibm.com/developerworks/linux/library/l-cpufreq-2/
Folks, in my application I'm using clock_gettime(CLOCK_MONOTONIC) in order to measure the delta time between frames (a typical approach in gamedev) and from time to time I'm facing a strange behavior of clock_gettime(..) - returned values occasionally are not monotonic (i.e prev. time is bigger than current time).
Currently, if such a paradox happens I simply skip the current frame and start processing the next one.
The question is how can this be possible at all? Is it a bug in Linux POSIX implementation of clock_gettime? I'm using Ubuntu Server Edition 10.04 (kernel 2.6.32-24, x86_64), gcc-4.4.3.
man clock_gettime says:
CLOCK_MONOTONIC_RAW (since Linux 2.6.28; Linux-specific)
Similar to CLOCK_MONOTONIC, but provides access to a raw hardware-based time that is not subject to NTP adjustments.
Since CLOCK_MONOTONIC_RAW is not subject of NTP adjustments, I guess CLOCK_MONOTONIC could be.
We had similar problems with Redhat Enterprise 5.0 with 2.6.18 kernel and some specific Itanium processor. We couldn't reproduce it with other processor on the same OS. It was fixed in RHEL 5.3 with slightly newer kernel and some Redhat patches.
Looks like an instance of
commit 0696b711e4be45fa104c12329f617beb29c03f78
Author: Lin Ming <ming.m.lin#intel.com>
Date: Tue Nov 17 13:49:50 2009 +0800
timekeeping: Fix clock_gettime vsyscall time warp
Since commit 0a544198 "timekeeping: Move NTP adjusted clock
multiplier to struct timekeeper" the clock multiplier of vsyscall is updated with
the unmodified clock multiplier of the clock source and not with the
NTP adjusted multiplier of the timekeeper.
This causes user space observerable time warps:
new CLOCK-warp maximum: 120 nsecs, 00000025c337c537 -> 00000025c337c4bf
See here for a patch. This was included into 2.6.32.19, but may not have been backported by the Debian team(?). You should check it out.
Try CLOCK_MONOTONIC_RAW.
Sure sounds like a bug to me. Perhaps you should report it in Ubuntu's bug tracker.
It's a linux bug. No ajustment in a monotonic clock can make it go backwards. You're using a very old kernel and a very old distribution.
Edit: are you sure you need to skip the frame ? If you call clock_gettime again, what happens ?