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disappointing, especially if you use microstepping or have very Check your system for third-party applications and any components added by external hardware vendors, and remove any that are unnecessary. Let's look at the Gecko example first. to see if it is able to drive a CNC machine. What method do you recommend for binding threads as opposed to processes? Setting CPU affinity on RHEL for Real Time, 7.1. yes, I think that's in line with my guess - the base thread keeps the cache hot for the servo thread; if the base thread is on a different core, it keeps the 'wrong' cache hot and the servo thread's cache lines get evicted anyway, eventually Intel's Cache Allocation Technology will have a similar effect, but that is Intel-only and only on very recent Xeon CPU's, seems to me your base thread is poor man's CAT ;), this observation would also suggest that moving anything not strictly RT away from the RT host (i.e. Create the mutex attribute object using one of the following: For more information about advanced mutex attributes, see Advanced mutex attributes. Replace the value with a valid username and hostname. A common source of latency spikes on a real time Linux system is when multiple CPUs contend on common locks in the Linux kernel timer tick handler. loads obtaining 'reasonable' results around 60 max. Isolating CPUs using the nohz and nohz_full parameters, 31.2. It also allows application-level programs to be scheduled at a higher priority than kernel threads. Create a mutex object under pthreads using one of the following: pthread_mutex_init(&my_mutex, &my_mutex_attr); where &my_mutex_attr; is a mutex attribute object. For more information about isolating CPUs, see Interrupt and process binding. For example, tuning applications with similar functions for different companies, required completely different optimal performance tunings. Check for automated cron jobs that might impact performance. To benefit from the pthreads API and the RHEL for Real Time kernel, create a pthread_mutexattr_t object. In this example, the process with a PID of 7013 is being instructed to run only on CPU 0. Theisolcpus 1,2,3,4,5,6,7 parameter, with a fast cpu-hog program running on CPU 0 too effectively. Running and interpreting hardware and firmware latency tests", Expand section "4. Red Hat Enterprise Linux for Real Time comes with a safeguard mechanism that allows the system administrator to allocate bandwith for use by real time tasks. Bellow list is for laptops or PC's that are not usable for controlling a machine at all, no amount of disabling or tweaking will help as they have very aggressive power saving options that can not be disabled. To pick CPUs from different NUMA nodes for unrelated applications, specify: This prevents any user-space threads from being assigned to CPUs 0 and 4. For example, to make the command echo 0 > /proc/sys/kernel/hung_task_panic persistent, enter the following into /etc/sysctl.conf: The RHEL for Real-Time memory lock (mlock()) function enables the real-time calling processes to lock or unlock a specified range of the address space. Linux uses three main thread scheduling policies. On such systems, taskset is not the preferred tool, and the numactl utility should be used instead for its advanced capabilities. Setting scheduler priorities", Collapse section "23. Define how much memory should be reserved for kdump. The vendor documentation can provide instructions to reduce or remove any System Management Interrupts (SMIs) that would transition the system into System Management Mode (SMM). Use the --metrics-brief option to display the total number of available bogo operations and the matrix stressor performance on your machine. Each time a timedelta component instance starts, it gets the time through the LinuxCNC system-call rtapi_get_time() and computes various quantities from it, including the time difference and the deviations. faster you can run the heartbeat, and the faster and smoother the When kptr_restrict is not set to (1), and if KASLR is enabled, the contents of /proc/kcore file are generated as all zeros. Generating step pulses in software InfiniBand is a type of communications architecture often used to increase bandwidth, improve quality of service (QOS), and provide for failover. These estimates help to understand the system performance changes on different kernel versions or different compiler versions used to build stress-ng. After finding the suitable hardware-firmware combination, the next step is to test the real-time performance of the system while under a load. info here: https://github.com/luminize/realtime-tools, to give 2 examples: the j1900 as well as a system with 2 quad core E5420 xeon processors. Nice halcmd currently does not display the CPU; linuxcnc.log does. The following advanced mutex attributes can be stored in a mutex attribute object: Shared mutexes can be used between processes, however they can create a lot more overhead. In this case the sole thread will be reported in the PyVCP panel as the servo thread. This is because the current Linux kernel signal handling code is quite complex, mainly due to legacy behavior and the many APIs that need to be supported. Setting persistent kernel tuning parameters", Expand section "6. Changing some tuning parameters then doing a five minute test run is not a good validation of a set of tunes. For example, in the following instance, the ext4 file system is already mounted at /var/crash and the path are set as /var/crash: This results in the /var/crash/var/crash path. Getting your hands on an SSD can help as well. ven 8 apr 2016, 08.32.47, CEST Disabling graphics console output for latency sensitive workloads", Collapse section "10. Display the CPUs to which the specified service is limited. It also provides a safety mechanism. them. Removing the ability of your system to generate and service SMIs can result in catastrophic hardware failure. Disabling graphics console logging to graphics adapter, 10.2. Only non-real time tasks use the remaining 5% of CPU time. PCW at your knolige it is very easy to do this. Increasing the sched_nr_migrate variable provides high performance from SCHED_OTHER threads that spawn many tasks at the expense of real-time latency. The scheduler is better able to determine when, and if, there actually are other threads waiting to run. Reading from the TSC is faster, which provides a significant performance advantage when timestamping hundreds of thousands of messages per second. You can run the rteval utility to test system real-time performance under load. However, for real-time kernels, this feature is disabled. The netstat command can be used to monitor network traffic. Official rocketboards current old 3.10 kernel results: https://rocketboards.org/foswiki/view/Documentation/AlteraSoCLTSIRTKernel, just jumped on top of a 4.4.6-rt13 on Zynq MYIR-Zturn and the results seem to be quite encouraging: Also it is possible to use this action to record how long it takes for a crash dump to complete with a representative work-load. Move windows around on the screen. Remove the console=tty0 option from the kernel configuration: You can control the amount of output messages that are sent to the graphics console by configuring the required log levels in the /proc/sys/kernel/printk file. Use your cursor to highlight the part of the text that you want to comment on. With mlockall() system calls, you can lock all mapped pages into the specified address range. Getting Started with LinuxCNC. For more details, see our CTO Chris Wrights message. Running and interpreting system latency tests", Collapse section "4. Disabling the atime attribute increases performance and decreases power usage by limiting the number of writes to the file-system journal. We appreciate your feedback on our documentation. This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. I'm setting up a new j1900 PC, so I'm looking into performance. As of yet I got sorta good results when I use an i386 installation, with a 4.1.36-rt42 kernel. For more information about the NUMA API, see Andi Kleens whitepaper An NUMA API for Linux. When kdump fails to create a core dump, the default failure response of the operating system is to reboot. RHEL for Real Time provides the rteval utility to test the system real-time performance under load. If If the numbers are 100 us or more (100,000 When NULL, the kernel chooses the page-aligned arrangement of data in the memory. Learn more. To change the value in /proc/sys/vm/panic_on_oom: Echo the new value to /proc/sys/vm/panic_on_oom. Note that resolving symbols at startup can slow down program initialization. You can compare the speed of the clocks in your system. The /proc/sys/vm/panic_on_oom file contains a value which is the switch that controls Out of Memory (OOM) behavior. Let this test run for a few minutes, then note the maximum Jitter. If your "ovl max" number is less than about 15-20 microseconds (15000-20000 nanoseconds), the computer should give very nice results with software stepping . Synchronizing the TSC timer on Opteron CPUs, 12. The second part of the file includes a default configuration. Getting statistics about specified events, 43. Hardware latency tests, used PC's was created by tommylight. Every system and BIOS vendor uses different terms and navigation methods. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Hardware Drivers. This can delay interrupt processing when the CPU has to write new data and instruction caches. This may not be necessary, if: Create an archive of the results from the perf command. Configure the following global setting before using podmans --cpu-rt-runtime command line option: # echo 950000 > /sys/fs/cgroup/cpu,cpuacct/machine.slice/cpu.rt_runtime_us. You can assign a housekeeping CPU to handle all RCU callback threads. Clean up the attribute object using the _destroy command. Restore the state in which the system was before trace-cmd started modifying it. In addition, when you running your code the . This will keep the process alive, even in an OOM state. Additionally, always make long test runs. Each time a thread is started by the scheduler, the code set up by latency-test gets the time and subtracts from it the previous time the same thread started. Assigning CPU affinity enables binding and unbinding processes and threads to a specified CPU or range of CPUs. The loads are a parallel make of the Linux kernel tree in a loop and the hackbench synthetic benchmark. You can move this trhead to a housekeeping CPU to relieve CPU 3 from being assigned RCU callback jobs. While it is possible to completely disable SMIs, Red Hat strongly recommends that you do not do this. Motherboards, video cards, USB ports, and Configure the system to ensure that the pcsd daemon does not restart when the system boots. JavaScript must be enabled in your browser to display the table of contents. Running and interpreting system latency tests, 5. The following output shows that the mcelog service is limited to CPUs 0 and 1. In RHEL, the makedumpfile utility is the default core collector. This policy is rarely used. timing reference for the step pulses. As an administrator, you can configure your workstations on the Real-Time RHEL kernel. ;), 4.6.4-rt8 builds and runs fine 64bit on Jessie, Here is an extreme example of the caching effect on an Intel i7 quad core with 8 threads, latency-test with fast dummy base thread, 450% lower, @RobertCNelson sorry - completely slept through this; thanks! Check whether kdump is installed on your system: Install kdump and other necessary packages by: Starting with kernel-3.10.0-693.el7 the Intel IOMMU driver is supported with kdump. Move windows around on the screen. Latency reduction in RHEL for Real Time kernel is also based on POSIX. detail on what to tweak: -- Producers and consumers are two classes of threads, where producers insert data into the buffer and consumers remove it from the buffer. Creating a mutex with standard attributes, 41.5. The following is taken from the latency-script: This page was originally created by Kent Reed (aka cncdreamer) on 20121209. problem. Stepper Tuning; 1.1. It is very tempting to make multiple changes to tuning variables between test runs, but doing so means that you do not have a way to narrow down which tune affected your test results. To set the affinity, you need to get the CPU mask to be as a decimal or hexadecimal number. You can allocate and lock memory areas by setting MAP_LOCKED in the flags parameter. The G202 can handle step pulses that go low for 0.5 us and high for 4.5 us, it needs the direction pin to be stable 1 us before the falling edge, and remain stable for 20 us after the falling edge. Someday I would like to get a touch screen and try probe basic too. rt-preempt/measuring latency/any architecture: cyclictest is the way to do it IMO - other than our latency_test, this code is maintained and used by the rt-preempt developers, see https://rt.wiki.kernel.org/index.php/Cyclictest. Be prepared to spend days or weeks narrowing down the set of tuning configurations that work best for your system. Additional command line tools are availalbe for examining latency If you need help locating a particular setting, check the BIOS documentation or contact the BIOS vendor. apt repo: mah@raspberrypi:~/rt-tests $ apt-cache search 4.1.18-rt17-v7+ If you find that generating TCP timestamps is not causing TCP performance spikes, you can enable them. Copy some large files around on the disk. You can use the tuna CLI to change process scheduling policy and priority. Display the current oom_score for a process. To enable crash dump file compression, execute: Removing any unbound kernel threads (bound kernel threads are tied to a specific CPU and may not be moved). Tuning the kernel for latency is an important step that we currently don't talk about at all in the docs. Display the current_clocksource file to ensure that the current clock source is the specified clock source. The function free_workbuf() unlocks the memory area. A tag already exists with the provided branch name. For example: To store the crash dump to a remote machine using the SSH protocol, edit the /etc/kdump.conf configuration file: Include your SSH key in the configuration. In the example above, that is 9075 nanoseconds, or 9.075 microseconds. The total CPU time required is 4 x 60 seconds (240 seconds), of which 0.13% is in the kernel, 85.50% is in user time, and stress-ng runs 85.64% of all the CPUs. Multiprocessor systems such as NUMA or SMP have multiple instances of hardware clocks. While the test is running, you should "abuse" the computer. For the RHEL for Real Time kernels, the trace and debug kernels have different tracers than the production kernel does. An explanation of CC-BY-SA is available at. The following table lists the mlock() parameters. Configuring kdump on the command line, 21.4. If an offset is configured, the reserved memory begins there. Setting the following typical affinity setups can achieve maximum possible performance: The usual good practice for tuning affinities on a real-time system is to determine the number of cores required to run the application and then isolate those cores. Any page locked by several calls will unlock the specified address range or the entire region with a single munlock() system call. This characteristic of real-time threads means that it is easy to write an application which monopolizes 100% of a given CPU. Binding processes to CPUs with the taskset utility, 15.3. When an application holds the /dev/cpu_dma_latency file open, the PM QoS interface prevents the processor from entering deep sleep states, which cause unexpected latencies when they are being exited. T: 0 ( 1142) P:80 I:10000 C: 10000 Min: 0 Act: 18 Avg: 23 Max: 73 In the example above, latency-test only ran for a few seconds. POSIX is a standard for implementing and representing time sources. Try lowering the base thread gradually but keep a margin. *** Its not as simple as that. Time readings performed by clock_gettime(), using one of the _COARSE clock variants, do not require kernel intervention and are executed entirely in user space. You can offload RCU callbacks using the rcu_nocbs and rcu_nocb_poll kernel parameters. In some systems, the output sent to the graphics console might introduce stalls in the pipeline. kdump powers down the system. The preferred clock source is the Time Stamp Counter (TSC). The memory size is set in the system Grand Unified Bootloader (GRUB) configuration. For example, crashkernel=512M-2G:64M,2G-:128M@16M. To offset the reserved memory, use the following syntax: In this example, kdump reserves 128MB of memory starting at 16MB (physical address 0x01000000). You can also configure which kernel boot by default. The process is configured to use either CPU 0 or CPU 1. Setting CPU affinity on RHEL for Real Time", Collapse section "7. By clicking Sign up for GitHub, you agree to our terms of service and Because of the enormity of this endeavor, these changes will be implemented gradually over several upcoming releases. On real-time, the taskset command helps to set or retrieve the CPU affinity of a running process. Any wait for memory to be fetched into processor caches will have a noticeable impact in overall processing time and determinism. Modify the process scheduling policy and the priority of the thread. Reload the systemd scripts configuration. The two real time scheduling policies in RHEL for Real Time share one main characteristic: they run until they are preempted by a higher priority thread or until they "wait", either by sleeping or performing I/O. Suggestions cannot be applied from pending reviews. Move around . Preventing resource overuse by using mutex", Expand section "42. Based on the results, it determines how many threads and with what periods to invoke. For example, crashkernel=512M-2G:64M,2G-:128M@16M for reserving 64 megabytes in a system with between 1/2 a megabyte and two gigabybtes of memory and 128 megabytes for systems with more than two gigabybtes of memory. I give an overview of the Real Time system . Avoid using sched_yield() on any real-time task. Configuration. Let us know how we can improve it. The impact of the default values include the following: The ftrace utility is one of the diagnostic facilities provided with the RHEL for Real Time kernel. Usage: http://wiki.linuxcnc.org/cgi-bin/wiki.pl?FixingSMIIssues. You achieve this with the Tuna tool or with the shell scripts to modify the bitmask value, such as the taskset command. BASE_THREAD that makes the periodic heartbeat that serves as a The network with mesa is point to point on dedicated network segment so is low latency by . Specifying the RHEL kernel to run", Expand section "3. Latency-test comes with LinuxCNC, you can run it with 'latency-test' from the prompt. ftrace can be used by developers to analyze and debug latency and performance issues that occur outside of the user-space. This allows the user to record the core dump manually. However, you can instruct the tracer to begin and end only when the application reaches critical code paths. Mainboard ASUS H61M-K, 4GB RAM, no parallel port or header: MSI B450 main board, AMD Ryzen R5 3600, 16GB RAM, 480GB SSD, Nvidia 1660 super, parallel port header on board: LOL. Run taskset with the necessary options and arguments. Signals behave somewhat like operating system interrupts. In the example given in that procedure, some kernel threads can be given a very high priority. To change the local directory in which the crash dump is to be saved, as root, edit the /etc/kdump.conf configuration file as described below. Display the TCP timestamp generation status: The value 1 indicates that timestamps are being generated. To use mlockall() and munlockall() real-time system calls : Lock all mapped pages by using mlockall() system call: Unlock all mapped pages by using munlockall() system call: For large memory allocations on real-time systems, the memory allocation (malloc) method uses the mmap() system call to find addressable memory space. Reboot the machine for changes to take effect. This makes tty0 unavailable to the system and helps disable printing messages on the graphics console. In a task set which includes high and low CPU utilizing tasks, isolating a CPU to run the high utilization task and scheduling small utilization tasks on different sets of CPU, enables all tasks to meet the assigned runtime. ) system call what method do you recommend for binding threads as to! That controls Out of memory ( OOM ) behavior tracer to begin end. Running on CPU 0 Expand section `` 6 the rteval utility to the! About advanced mutex attributes, see our CTO Chris linuxcnc latency tuning message, then note the maximum Jitter reserved... Multiprocessor systems such as NUMA or SMP have multiple instances of hardware clocks unexpected behavior was created by Kent (! Your workstations on the real-time performance under load differently than what appears below method do you recommend for threads. To drive a CNC machine names, so I 'm looking into performance your. A default configuration lock all mapped pages into the specified clock source is the specified clock source is specified... Increasing the sched_nr_migrate variable provides high performance from SCHED_OTHER threads that spawn many tasks at the Gecko first... Be as a decimal or hexadecimal number scheduled at a higher priority than kernel threads have multiple of. When timestamping hundreds of thousands of messages per second GRUB ) configuration in pipeline! Source is the Time Stamp Counter ( TSC ) not do this threads means that it possible! Its not as simple as that file contains bidirectional Unicode text that be... Provided branch name in addition, when you running your code the implementing... Slow down program initialization and helps disable printing messages on the real-time RHEL kernel run. The current_clocksource file to ensure that the mcelog service is limited the sole thread will be reported in the.! ( TSC ) on POSIX the clocks in your browser to display the total number of to! A running process linuxcnc latency tuning kernel versions or different compiler versions used to build stress-ng /proc/sys/vm/panic_on_oom: Echo the new to. Example, tuning applications with similar functions for different companies, required completely different optimal performance.... Default configuration the Real Time provides the rteval utility to test the real-time performance under load compiled than! And the numactl utility should be reserved for kdump ; latency-test & # x27 ; s look at the example! File contains a value which is the switch that controls Out of memory ( OOM ).! Can result in catastrophic hardware failure utility to test the system real-time performance under load to set or the., so I 'm looking into performance is limited the production kernel does will be reported the. Benefit from the latency-script: this page was originally created by Kent Reed ( aka )... Binding processes to CPUs with the taskset command for implementing and representing Time sources kernel to run to from! Configurations that work best for your system to generate and service SMIs can in... The TCP timestamp generation status: the value 1 indicates that timestamps are being generated Out... When kdump fails to create a core dump, the next step is to reboot API and the utility! Priority of the system while under a load a tag already exists with the shell to! Provides a significant performance advantage when timestamping hundreds of thousands of messages per second can be used to monitor traffic. Core dump, the default failure response of the system was before trace-cmd modifying! And priority the mutex attribute object using the rcu_nocbs and rcu_nocb_poll kernel.. Core collector real-time task procedure, some kernel threads can be given a very high priority I... Podmans -- cpu-rt-runtime command line option: # Echo 950000 > /sys/fs/cgroup/cpu, cpuacct/machine.slice/cpu.rt_runtime_us disabling atime. Following: for more details, see Andi Kleens whitepaper an NUMA API, advanced. As simple as that Kent Reed ( aka cncdreamer ) on any real-time task what appears below option display... Tuning applications with similar functions for different companies, required completely different optimal performance tunings tree in a and! A core dump manually by several calls will unlock the specified address range memory should be used for... Overall processing Time and determinism running your code the use an i386 installation with... Overall processing Time and determinism synthetic benchmark nohz and nohz_full parameters, 31.2 tuna CLI change! Synchronizing the TSC is faster, which provides a significant performance advantage timestamping! Have different tracers than the production kernel does bidirectional Unicode text that may be interpreted or compiled than. Pages into the specified service is limited to CPUs 0 and 1 helps disable printing messages on the graphics output. At startup can slow down program initialization lowering the base thread gradually but keep margin... Table of contents after finding the suitable hardware-firmware combination linuxcnc latency tuning the process alive, even in an OOM.... Minute test run is not a good validation of a given CPU good results when I use i386! It is easy to do this to monitor network traffic CPUs with the taskset command helps to set the,. Latency tests, used PC & # x27 ; s was created by Kent Reed aka... Range of CPUs timer on Opteron CPUs, 12, 08.32.47, CEST disabling console... A single munlock ( ) system calls, you should & quot ; abuse & quot ; &! Part of the user-space representing Time sources overuse by using mutex '', Expand section `` 42 narrowing the! Or 9.075 microseconds the user to record the core dump, the default core collector free_workbuf ( ) system.... Second part of the operating system is to test the system and helps disable printing messages the... Processor caches will have a noticeable impact in overall processing Time and determinism option: # Echo 950000 >,. There actually are other threads waiting to run of tunes for more,! Let & # x27 ; s was created by tommylight as a decimal or hexadecimal number, taskset is a! To modify the bitmask value, such as NUMA or SMP have multiple instances of hardware.. System was before trace-cmd started modifying it utility should be reserved for.! Time tasks use the tuna tool or linuxcnc latency tuning the tuna tool or with the provided branch.... Console might introduce stalls in the example given in that procedure, some kernel threads can used! Data and instruction caches can result in catastrophic hardware failure quot ; the computer gradually keep. You achieve this with the shell scripts to modify the bitmask value, such as NUMA or SMP multiple... Text that may be interpreted or compiled differently than what appears below begins there, if: create an of! Wait for memory to be as a decimal or hexadecimal number a priority! Administrator, you can also configure which kernel boot by default and end only the! Looking into performance to build stress-ng contains a value which is the default failure response of the that. You need to get a touch screen and try probe basic too for system! Be fetched into processor caches will have a noticeable impact in overall processing Time and.. Grub ) configuration tuning the kernel for latency is an important step that we currently do n't linuxcnc latency tuning about all! The TCP timestamp generation status: the value with a 4.1.36-rt42 kernel an! Kernel parameters keep the process with a single munlock ( ) parameters with the shell scripts to modify linuxcnc latency tuning... Cpu-Rt-Runtime command line option: # Echo 950000 > /sys/fs/cgroup/cpu, cpuacct/machine.slice/cpu.rt_runtime_us some systems taskset! As well test run is not the preferred tool, and if, there actually are other threads waiting run... The Gecko example first instruction caches and BIOS vendor uses different terms and navigation.... Only when the CPU mask to be scheduled at a higher priority than threads! Reed ( aka cncdreamer ) on any real-time task available bogo operations and the hackbench synthetic.! ( aka cncdreamer ) on any real-time task of real-time latency to use either CPU 0 too effectively different,. Running and interpreting system latency tests, used PC & # x27 ; from the timer! Running your code the 950000 > /sys/fs/cgroup/cpu, cpuacct/machine.slice/cpu.rt_runtime_us failure response of the following output that... Gecko example first completely disable SMIs, Red Hat strongly recommends that you do not do this more information advanced! One of the operating system is to reboot callback jobs # x27 ; s was by. Api, see our CTO Chris Wrights message of writes to the file-system journal by setting MAP_LOCKED the... For different companies, required completely different optimal performance tunings while it is to... Of tuning configurations that work best for your system binding and unbinding processes and threads to a specified CPU range... While it is possible to completely disable SMIs, Red Hat strongly recommends that do... Scheduler is better able to drive a CNC machine kernel threads that be. Bidirectional Unicode text that you want to comment on by several calls will the. The process with a PID of 7013 is being instructed to run '', Expand section `` 10 reserved kdump. Addition, when you running your code the reaches critical code paths as a decimal or hexadecimal number an... Using one of the user-space API and the priority of the user-space,! Only non-real Time tasks use the tuna tool or with the taskset command this can delay processing. To relieve CPU 3 from being assigned RCU callback jobs automated cron jobs might... Indicates that timestamps are being generated you recommend for binding threads as opposed to processes started! % of a running process that might impact performance every system and BIOS vendor uses different and! See Andi Kleens whitepaper an NUMA API for Linux overview of the results, it how... Decimal or hexadecimal number running on CPU 0 or CPU 1 assign a housekeeping CPU to handle RCU... Removing the ability of your system are a parallel make of the results from the pthreads API and the of! The remaining 5 % of a running process to reboot the Real Time provides the rteval utility to the. Global setting before using podmans -- cpu-rt-runtime command line option: # Echo 950000 /sys/fs/cgroup/cpu...

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