Questions tagged [real-time]

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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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21 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
58 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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13 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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110 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
31 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
201 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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45 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
298 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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0answers
47 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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16 views

How to track a file for processes that use this file

I have a script, that listens for file /lib/modules/4.10.0-19-generic/kernel/drivers/media/usb/uvc/uvcvideo.ko and if the file is been accessed then runs the lsof command: #!/bin/sh inotifywait -mrq -...
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282 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
210 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
650 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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29 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
331 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
551 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
293 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
53 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
625 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
95 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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80 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
533 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
709 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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2answers
16k 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
487 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
364 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
372 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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306 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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92 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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3answers
6k 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
435 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
175 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 ...
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117 views

rtcwake being set one day ahead of intended time

I am trying to use this command to wake up my computer 5 seconds from now: sudo rtcwake -m no -s 5 The problem I am having is that the time to wake my computer is set 5 seconds ahead of current time ...
3
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1answer
1k views

Docker with real-time / low-latency audio? (for virtual amps like Guitarix…)

I've been trying to get a foss virtual guitar amp to run on my Fedora machine for a while now, Guitarix (which runs on JACK) to be more precise. But I just can't figure it out. People say that it is ...
2
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1answer
265 views

lxc and sched_setscheduler

I am trying to run an application inside a Centos container and needs to run in real time. I googled around and the suggestion was to add lxc.cap.keep = sys_nice. After I did it, lxc-start complains ...
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0answers
76 views

Time between process runs is occasionally too long, how can I set a maximum time? [closed]

I am using a raspberry pi to grab data through a SPI port. Attached to the SPI port is a PIC, programmed so that it samples on an A/D at 12.8kHz, and stores the samples in a 256 long buffer. (to cope ...
2
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1answer
1k views

Clock instability in Debian 9 (stretch)

I have a machine running Debian 8 (jessie) downgraded to kernel 3.2-rt. This is running an application which is set to realtime priority (SCHED_RR), wakes up every 1ms to do some processing, and ...
3
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1answer
3k views

How to run real-time application in Linux?

Trying to get working LinuxCNC on my Debian Jessie, I did: Installed the kernel 4.9 RT through Jessie backport using apt-get/aptitude. Restarted my computer and checked uname -a contain PREEMPT RT ...
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186 views

Raspberry Pi RT Preempt Linux Kernel Build Error

I am trying to Build and install a Raspberry Pi RT Preempt Linux Kernel. These are the steps that I had followed: I installed the pre-compiled kernel kernel-4.4.9-rt17.tgz I downloaded Raspberry Pi ...
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1answer
112 views

systemd: start openvpn.service after time has synced

I use systemd-timesyncd to sync the time on my system. It doesn't have a battery to save the RTC. When I connect it to the internet it takes about 30 seconds to sync the time. I would like to reduce ...
2
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1answer
682 views

Can SCHED_FIFO be preempted by SCHED_DEADLINE?

As stated in the man pages: A SCHED_FIFO thread runs until either it is blocked by an I/O request, it is preempted by a higher priority thread, or it calls sched_yield(2). From the same source: ...
3
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1answer
105 views

Is possible to focus single core on very realtime calculations while using others as regular cores?

I am finishing part of project I started while ago and I need decent kernel for it. There is code that is critical to be ran all the time, as latency bigger than 1us may have impact on quality of ...
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1answer
86 views

Make Linux responding even when there is an I/O Error

WHen there are harddisk's I/O error, my computer becomes unresponsive (mouse cannot be moved, screen freezes for a moment, keypress does nothing), for example when executing: sudo fsck.ext4 -fckyvt /...
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0answers
264 views

VM and host time drift during suspend

I am running Ubuntu 16.04 on my laptop, with Ubuntu 14.04 in a Vagrant VM in VirtualBox. My laptop is running SystemD and network time is enabled: naftuli@reprisal:~$ sudo timedatectl status ...
4
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1answer
1k views

realtime pthread created from non-realtime thread with init.d

I have a piece of C++ code that runs just fine when I run it from a Linux terminal, but which throws an EPERM error when run from a SystemV (init.d) script on bootup. The error comes from a ...
4
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1answer
1k views

Record time of every process or thread context switch

I'm trying to get the nearest to real-time processing I can with a Raspbian distribution on a Raspberry Pi for manipulating its GPIO pins. I want to get a "feel" for the kind of performance I can ...
3
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1answer
3k views

“tail -f” using “tcpdump -r”

To display content of pcap file , we use : tcpdump -r /Path/to/syscontection.pcap; However, this command line does not follow the pcap file on realtime , like tail -f which follows a plain text . ...
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0answers
109 views

How to install real time patch on Embedded Linux version 3.16.0

I have a microprocessor that runs the embedded linux version 3.16.0-rc3 (armsdk@debian, gcc version 4.7.2 (GCC)). I wanted to install a real time patch, but I did not find the one for my linux version....