Questions tagged [real-time]

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Mysterious issue with the 5.10.7-3 Linux Kernel

For the last month or so, I've been getting a very weird issue pretty much daily. I would be using my system like usual, and the screen would just suddenly freeze. If there's audio playing, the last ...
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6 views

conflict : watching in realtime opened ports without line wrap

How to monitor ports and connection in real time in Arch linux ? I can use watch combine with ss -tulpn, but when pipe it to less -S (to disable line wrap), the output is nothing. $sudo watch ss -...
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1answer
36 views

Duplicating audio in pure ALSA for playback on local device and streaming via trx

I am trying to achieve a multi-room audio setup in my house using Raspberry Pis. How can I get VLC playing simultaneously out the local headphone port while also streaming it to other devices via trx? ...
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rtkit: list threads it is “supervising”?

rtkit obviously knows which threads it is "supervising", since it spams syslog with messages like rtkit-daemon[1277]: Supervising 3 threads of 2 processes of 1 users. However, the nefarious ...
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13 views

Any low-overhead busy waiting for short-latency notification over threads

Is there any busy waiting's alternative to gain both low CPU usage and short-latency notification over threads. If the thread is block by a semphore or signal, it will be swapped out from the core, ...
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2answers
115 views

Real-time patch on Linux 5.9.1 does not show fully-preemptible option for arm64 option

I am trying to get my own custom Real-time Linux on a Raspberry Pi 4B. My status is this: I built the Linux 5.9.1 version, and have my own version of U-Boot, RFS with which I am able to successfully ...
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2answers
170 views

How to start a realtime process?

I looking for a way to start a real-time process or set a running process as a real-time process.
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1answer
136 views

Install a real-time kernel on CentOS 7 i386

I have computer where I'm trying to install real-time kernel. My OS: # uname -a Linux localhost.localdomain 3.10.0-1127.el7.centos.plus.i686 #1 SMP Sun Apr 5 18:08:31 UTC 2020 i686 i686 i386 GNU/Linux ...
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2answers
64 views

What RT patch to use for a specific linux kernel version

Running the $uname -r command on my embedded device reveals my kernel to be 4.14.73-ltsi (it is a custom Linux kernel built for an embedded device). Now I intend to install the real time (RT) patch ...
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105 views

Linux Time persist through reboot issue

I have a custom board that houses a System on module(SOM) running linux kernel 4.4.15 The board has an RTC that is backed up via small battery. I have the board running with no network connection ...
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2answers
745 views

Trouble selecting “Fully Preemptible Kernel (Real-Time)” when configuring/compiling from source

I am trying to compile the 5.4 kernel with the latest stable PREEMPT_RT patch (5.4.28-rt19) but for some reason can't select the Fully Preemptible Kernel (RT) option inside make nconfig/menconfig. I'...
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What is UIE timer in RTC?

I am trying to apply a patch that enables UIE timer but I don't understand what UIE stands for and what's the use of it. https://lore.kernel.org/linux-rtc/20191021155631.3342-1-alexandre.belloni@...
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28 views

System becomes non interactive when multiple real time threads are run on limited number of CPUs

Linux arch 5.5.9-arch1-2 #1 SMP PREEMPT Thu, 12 Mar 2020 23:01:33 +0000 x86_64 GNU/Linux I have been experimenting with CPUs affinity and scheduling policies and there is one thing that has surprised ...
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1answer
3k views

Why is the integer value of SIGRTMIN (first real-time signal) 34 and not 32? [duplicate]

Examining the output of kill -l command $ kill -l 1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL 5) SIGTRAP 6) SIGABRT 7) SIGBUS 8) SIGFPE 9) SIGKILL 10) SIGUSR1 11) SIGSEGV 12) SIGUSR2 13) ...
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1answer
40 views

Linux read() system call sampling rate, task scheduling & RT_PREEMPT

I am working with a Measurement Computing PCIe-DAS1602/16 DAQ: https://www.mccdaq.com/pci-data-acquisition/PCIe-DAS1602-16.aspx with Linux device drivers written by Warren Jasper: https://github....
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92 views

How to delete or shrink compiled kernel installation directory and still build an external module?

I am having trouble building external modules after compiling the linux kernel on an external device. It is the 4.19.103 kernel with the real time patch-4.19.103. My onboard storage disk is <3Gb ...
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1answer
38 views

Cutting out specific text from specific lines in real time

So I have a log running in real time and saving to a text file named 'test.txt' also in real time. Now I want to set up a process that constantly polls that text file for changes and cuts out a ...
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80 views

faketime adjusting clock rate freezing graphical applications?

I am trying to trick Chromium to think time passes faster than it really does. One user suggested I use libfaketime. It works, almost. Specifying time shift works fine: faketime -f '+1y' chromium-...
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94 views

How does the SCHED_DEADLINE runtime overrun signal (SIGXCPU) work?

I'm implementing a rt-thread using SCHED_DEADLINE. I'm trying to catch a SIGXCPU-signal, if the thread exceeds the specified sched_runtime. To my understanding of the manpage, this can be achived by ...
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1answer
66 views

Change perception of real time for one process

I would like to change the perception of real time for one process. Making the process believe that time is passing at 50% or 150% of the speed my system/kernel/hardware-clock thinks. I'd like to ...
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18 views

Strange ping latency

We have a complex real time application running RHEL 7.4 on ESX as a virtual machine. The VM is hosted on a large NAS-storage. Currently we have repeated latency bursts also evidenced in a running ...
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1answer
192 views

Inconsistent CPU Usage in Top

I'm experiencing very strange behaviour with some hardware we're working on. My setup consists of Linux 4.9.87 w/ SMP & PREEMPT RT on a dual-core iMX6 CPU. The application running on this setup ...
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1answer
174 views

SCHED_RR and SCHED_FIFO only work on “prempt kernal”?

I am running a python program on the raspberry Pi (Raspbian) that I would like to give higher priority. I want to run the following command : $ sudo chrt --rr 50 python3 loopExample.py I have read ...
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1answer
576 views

Why does /proc/stat count more than 100 tick/s

I have a developer complaining that the CPU usage reported by /proc/stat is not consistent. It is my understanding that /proc/stat is counting ticks, which since kernel 2.6 has been fixed to 100/s ...
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118 views

When are audio threads preempted?

In audio threads, I've been told it's good style to not use syscalls like e.g. printf() because they give control back to the kernel, which can then decide to continue with another thread, which means ...
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1answer
643 views

Available options for real-time Linux (Centos 7) and their relation to one another [closed]

I'm looking to expand and also get more current information from the question asked here. I have a requirement for real-time behavior that has is sub-millisecond and am now exploring what my options ...
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64 views

Small delay in sudo

I want my zsh prompt to display whether the session has sudo rights (from a previously run sudo command). After looking at the answers to this question, I arranged to use the exit status of sudo -n ...
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1answer
832 views

How to set the SCHED_RR time slice or time quantum per process / thread?

The time slice (also called time quantum) for threads with SCHED_RR policy can, according to the sched_rr_get_interval man page be obtained using int sched_rr_get_interval(pid_t pid, struct timespec *...
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1answer
337 views

Realtime, SCHED_FIFO, CPU_SET()

I'm trying to assign two real time processes to two cpus(one each). I'm using SCHED_FIFO scheduling policy. I'm doing the following things: adding "quiet splash isolcpus = 6,7" at ...
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1answer
2k views

Detect if USB disk is mounted in C application in Linux

I would like to check if USB disk is mounted in a C application. I know that in a script I can accomplish this via mount | grep /mnt (the mount point where udev mounts the USB drive) but I need to do ...
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30 views

Filter output / print one record per event or time period

I've got a custom HID device which prints out exact coordinates of touched points at real time. It is very sensitive & currently printing out the coordinate that's being touched on multiple ...
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1answer
560 views

compile and use a realtime kernel on CentOS 7

I would like to compile and use a realtime kernel on CentOS 7. I found a guide on the web: http://jensd.be/589/linux/complile-and-use-a-realtime-kernel-on-centos-7-or-rhel-7 When I try to use it I ...
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1answer
1k views

Running make -j$(nproc) or make modules -j$(nproc)

I am following this. To run make -j$(nproc) make modules -j$(nproc) I know that make is running jobs Are the jobs supposed to run for hours? (I got impatient and interrupted.) make -j$(nproc)
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Activation /Config of Preempt RT [duplicate]

I installed the Preempt RT patch, how can I know if it was installed correctly, and if it was activated? If it was right, what configuration shall be done, and how to do it?
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1answer
398 views

Among these two in my ps output, which real-time process will be preempted over the other by linux?

I have got some idea from: https://stackoverflow.com/questions/8887531/which-real-time-priority-is-the-highest-priority-in-linux about how the real time priority values assigned to different ...
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1answer
58 views

Since which version does linux support system clock with nano precision?

We are using centos7 and with the date command we came to know that system clock support nano precision. date +"%s %9N" 1537941601 130559008 So, we were to know that from which version did linux ...
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1answer
1k views

Knowing when a write() on a serial port has finished transmitting data

I need to synchronize an IO pin value with a write to a serial port from user space (because I wasn't yet able to do it from kernel space - see my other question). My code (leaving out error checking) ...
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1answer
144 views

How to real-time display a number from a running log file or terminal [closed]

I have a CNC and the software runs from a terminal. I would like to catch the current Z axis depth in real-time to display it. The information I need is shown in the terminal as well as in the log ...
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0answers
92 views

Linux (kernel 3.x and 4.x) Pthread and general process scheduling algorithms

I was wondering if both scheduling (contention) scopes (SYSTEM and PROCESS) are used in the Linux kernel scheduling logic. POSIX supports PROCESS scope pthreads (MXN model) and SYSTEM scope pthreads (...
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1answer
808 views

CFS and real-time policies

I'm trying to implement a real-time algorithm in Linux. I've studied the linux Real-Time policies : sched_rr, sched_fifo. Than i go deeper and i found the Completely Fair Scheduler. I deduced that ...
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2answers
1k views

Port Forwarding without delay and high fps in a real time live stream using socat

I am using the command socat to port forward a connection from a real-time live stream. TCP4-LISTEN:8080 TCP4:123.456.789.12:80 The problem is it has added delay and low fps while the live stream ...
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4answers
36k views

Current time/date as a variable in BASH and stopping a program with a script

I am trying to create a raspberry pi spy cam bug. I am trying to make it so the new file created for the various processes come up with NOW=`date '+%F_%H:%M:%S'`; which works fine. but it requires ...
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1answer
692 views

Enable CONFIG_PREEMPT_RT_FULL after the kernel compilation

I have Linux with a kernel that was compiled with the real-time patch, but the config option CONFIG_PREEMPT_RT_FULL was not enabled (it says in /proc/config that it is not set). Do you now if there ...
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0answers
436 views

Check if Linux Kernel is real time or not from Kernel module

We have a kernel module which is used on both real time (RT) and non-real time Linux kernel. Module uses the function get_user_pages_remote. However, there is a version check since the module needs to ...
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1answer
544 views

Applying RT PREEMPT kernel patch fails

I am trying to apply the RT PREEMPT patch for the Linux kernel. As mentioned in guides like this and this, you are supposed to do it like this: zcat patch-4.14.15-rt13.patch.gz | patch -p1 (...
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391 views

Configure raspberry pi kernel from script instead of menuconfig

I would like to build the official kernel for the Raspberry Pi. But I want to change one feature during the process. I'm basically following this tutorial: http://www.frank-durr.de/?p=203 And at ...
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0answers
120 views

What are the performance implications of isolating a core vs PREEMPT_RT?

I try to figure out what the differences between several real time systems are. So far I've tried to use the PREEMPT_RT patch and to isolate a core and reserve it for the RT application. So far I've ...
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4answers
10k views

How to find scheduling policy and active processes' priority?

I want to make a shell script that finds all active processes and to print to the user the scheduling policy.I want the result to be like this. pid 3042's current scheduling policy: SCHED_OTHER pid ...
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2answers
839 views

Interpretation of PTP4L and PHC2SYS syslog records

I'm using the ptp4l and phc4sys services to syncronize the clocks of my Centos 7.4 servers to a central PTP source. The services regularly write syslog records like the one below. I haven't found any ...
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1answer
241 views

Where to find extended information about menuconfig kernel configuration options?

Where to find extended information about menuconfig options? I am especially interested in those related with improving latency/jitter of a RT_PREEMT kernel (apart of the obvious ...