Write the name of the clock source you want to use to the /sys/devices/system/clocksource/clocksource0/current_clocksource file. ), at 7000 latency most here woudt be in heven stepper systems run perfect on < 150k. This is a an a J1800. latency-plot makes a strip chart recording for a base and a servo thread. Transmitting packets more than once can cause delays. RedHat advise that system administrators regularly update and test kexec-tools in your normal kernel update cycle. The number of samples recorded by the test. Sign up for a free GitHub account to open an issue and contact its maintainers and the community. Memory locks do not stack. So IMHO we need to set up a "virtual" usage of the PC / Device for certain time and then start the test. This sends buffer writes to the kernel as soon as an event occurs. That is, TCP timestamps are enabled. You can assign a CPU to handle all RCU callbacks. The operating system scheduler uses this information to determine the threads and interrupts to run on a CPU. Any page locked by several calls will unlock the specified address range or the entire region with a single munlock() system call. 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. Ensure that the results file was created. Disabling graphics console output does not delete information. The preferred clock source is the Time Stamp Counter (TSC). The makedumpfile --mem-usage command estimates how much space the crash dump file requires. Not all hardware is equal, test different RAMs if you have available. It can be used in all processors. Note that resolving symbols at startup can slow down program initialization. You do not need to run any load on the system while running the hwlatdetect program, because the test is looking for latencies introduced by the hardware architecture or BIOS/EFI firmware. around on the disk. For example, to reserve 128MB of memory, use the following: Alternatively, you can set the amount of reserved memory to a variable depending on the total amount of installed memory. This procedure does not change any of the kernel tuning parameters in the current session. So I started playing around with gmoccapy, chnaged some code, compiled some stuff etc. To review, open the file in an editor that reveals hidden Unicode characters. Run a Latency Test . A cpu-hog thread with a SCHED_FIFO or SCHED_RR policy higher than the interrupt handler threads can prevent interrupt handlers from running. The process is configured to use either CPU 0 or CPU 1. For more information about isolating CPUs, see Interrupt and process binding. The wildcard cannot, however, be used inside a word. In either of these cases, no provision is made by the POSIX specifications that define the policies for allowing lower priority threads to get any CPU time. This might cause potential delay in task execution while waiting for data transfers. linux-image-rt-4.1.18-rt17-v7+ - Linux kernel, version 4.1.18-rt17-v7+, mah@raspberrypi:~/rt-tests $ sudo cyclictest -t1 -p 80 -n -i 10000 -l 10000, policy: fifo: loadavg: 0.33 0.25 0.15 1/179 1465, T: 0 ( 1462) P:80 I:10000 C: 10000 Min: 11 Act: 15 Avg: 14 Max: 42. As a result, the dedicated process can run as quickly as possible, while all other non-time-critical processes run on the other CPUs. Tomorrow i'll try the scenario you suggest to JavaScript must be enabled in your browser to display the table of contents. LinuxCNC on Raspberry Pi: How to Make It Work | All3DP. It generates a memory usage report. Move around . This priority is the default value for hardware-based interrupts. Surf the web. pthread_mutexattr_destroy(&my_mutex_attr); The mutex now operates as a regular pthread_mutex, and can be locked, unlocked, and destroyed as normal. It is recommended that you make the Real-Time kernel panic on OOM (1). Reboot the machine for changes to take effect. To do this, use the tuna command and move all RCU callbacks to the housekeeping CPU. I don't think the cpu hog and idle poll techniques are applicable to Preemt-RT (or were even a good idea when they were. Verify that the displayed value is lower than the previous value. (he default priority is 50. Making persistent kernel tuning parameter changes, 6. It may be useful to see spikes in latency when other applications are started or used. For more information, see Configuring InfiniBand and RDMA networks. Run an OpenGL program such as glxgears. This may not be necessary, if: Create an archive of the results from the perf command. Reduces timer activity on a particular set of CPUs. capable of outputting step pulses that are generated by the software. This is done by the FF1=1.00 PID term. Set the default kernel to the listed Real Time kernel. The --message-level option specifies message level as 1. This action confirms the validity of the configuration. This test is the first test that should be performed on a PC to see if it is able to drive a CNC machine. This stress test aims for low data cache misses. Refer to the man page, the HAL manual, or better yet the source code for details. Improving network latency using TCP_NODELAY", Collapse section "39. However, this comes with a high overhead cost. To stop the kdump service in the current session: It is recommended to set kptr_restrict=1. fine pitch leadscrews. The output displays the duration required to read the clock source 10 million times. You can configure the default boot kernel. The following provides instructions for avoiding OOM states on your system. Specify the Non-Uniform Memory Access (NUMA) memory nodes to use. This enables all real-time tasks to meet the scheduler deadline. In this example, my_embedded_process is being instructed to execute on processors 4, 5, 6, and 7 (using the hexadecimal version of the CPU mask). Set isolated_cores=cpulist to specify the CPUs that you want to isolate. Applications that require low latency on every packet sent must be run on sockets with the TCP_NODELAY option enabled. The file name is in the form rteval--N-tar.bz2, where is the date the report was generated, N is a counter for the Nth run on . View more information about the CPUs, such as the distance between nodes: The initial mechanism for isolating CPUs is specifying the boot parameter isolcpus=cpulist on the kernel boot command line. You can either specify the crashkernel= value or configure the auto option. For more information, refer to the devices' documentation. The network with mesa is point to point on dedicated network segment so is low latency by . Using mlock() system calls to lock pages, 6.3. Typically, syslogd logs to a local file, but it can also be configured to log over a network to a remote logging server. As a result, journaling file systems can slow down the system. If hwlatdetect shows that the system cannot meet the latency requirements of the application, try changing the BIOS settings or working with the system vendor to get new firmware that meets the latency requirements of the application. When the call returns successfully, all pages that contain a part of the specified address range stay in the memory until unlocked later. idle=poll prevents the processor from entering the idle state. SCHED_RR is a modification of SCHED_FIFO. This causes programs waiting for data signaled by those interrupts to be starved and fail. This section provides information about real time scheduling issues and the available solutions. Open the /etc/fstab file using your chosen text editor and locate the entry for the root mount point. Run hwlatdetect, specifying the test duration in seconds. If you purchase using a shopping link, we may earn a commission. Stress testing real-time systems with stress-ng", Collapse section "43. For examplem, the operating system is responsible for managing both system-wide and per-CPU resources and must periodically examine data structures describing these resources and perform housekeeping activities with them. Any thread created as a SCHED_FIFO thread has a fixed priority and will run until it is blocked or preempted by a higher priority thread. I have noticed that on some systems opening a file can cause a jump in latency. Setting processor affinity using the sched_setaffinity() system call, 7.3. Each line shows the IRQ number, the number of interrupts that happened in each CPU, followed by the IRQ type and a description. This behavior is different from earlier releases of RHEL, where the directory was being created automatically if it did not exist when starting the service. Assigning the OTHER and NATCH scheduling policies does not require root permissions. Configure the machine to which the logs will be sent. Unit configuration directives are used to change the priority of a service during boot process. Configure the desired log level in the /proc/sys/kernel/printk file. the difference between 1 and 2 are visible. The list of available clock sources in your system is in the /sys/devices/system/clocksource/clocksource0/available_clocksource file. Preventing resource overuse by using mutex, 41.3. 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. If you must change the default configuration, comment out the isolated_cores=${f:calc_isolated_cores:2} line in /etc/tuned/realtime-variables.conf configuration file and follow the procedure steps for Isolating CPUs using TuneDs isolated_cores option. You can boot any installed kernel, standard or Real Time. The -d option specifies dump level as 31. If this is your case, follow the procedure below. 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. Reload the systemd scripts configuration. 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. The FIFO and RR scheduling policies require a priority of 1 or more. Improving response time by configuring System Management Interrupts, 14. pthread_mutexattr_setprotocol(&my_mutex_attr, PTHREAD_PRIO_INHERIT); When a pthread dies, robust mutexes under the pthread are released. The following table lists the mlock() parameters. The standard test in LinuxCNC is checking the BASE period latency (even though we are not using a base period). Modern processors actively transition to higher power saving states (C-states) from lower states. Do not run LinuxCNC or Stepconf while the latency test is running. Finally, latency-test issues the command "halrun lat.hal" . kdump saves the crash dump file in /var/crash/var/crash directory, when the dump target is mounted at /var/crash and the option path is also set as /var/crash in the /etc/kdump.conf file. Play some music. As a result, the TSC on a single processor never increments at a different rate than the TSC on another processor. For more information about the NUMA API, see Andi Kleens whitepaper An NUMA API for Linux. One advantage of perf is that it is both kernel and architecture neutral. What Latency-Test Does. This is a journaling file system. Table14.1. The boot process priority change is done by using the following directives in the service section of /etc/systemd/system/service.system.d/priority.conf: Sets the CPU scheduling policy for executed processes. This provides a number of trace-cmd examples. A floating-point unit is the functional part of the processor that performs floating point arithmetic operations. To improve performance, you can change the clock source used to meet the minimum requirements of a real-time system. To give application threads the most execution time possible, you can isolate CPUs. The CONFIG_RT_GROUP_SCHED feature was developed independently of the PREEMPT_RT patchset used in the kernel-rt package and is intended to operate on real time processes on the main RHEL kernel. The -p or --pid option work an existing process and does not start a new task. This is in contrast to hardware clocks which are selected by the kernel and implemented across the system. When tuning the hardware and software for LinuxCNC and low latency there's a few things that might make all the difference. The sched_yield() behavior allows the task to wake up at the start of the next period. It is also tempting to make large changes when tuning, but it is almost always better to make incremental changes. In this example, my_embedded_process is being instructed to use only CPU 3 (using the decimal version of the CPU mask). In the default mode, it runs the specified stressor mechanisms in parallel. On 20 Nov 2015, at 11:55, Michael Haberler notifications@github.com wrote: mah@j1900:/next/home/mah/src/rt-tests-i386$ sudo cyclictest -t1 -p 80 -n -i 10000 -l 10000, policy: fifo: loadavg: 0.00 0.01 0.05 1/284 7160. Check the IRQs in use by each device by viewing the /proc/interrupts file. If the total amount of memory is more than 2GB, 128MB is reserved. In case of an error, they return -1 and set a errno to indicate the error. This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. Showing the layout of CPUs using lstopo-no-graphics. improvment on Zynq platforms but it should work also on other multiprocessor architectures). use software stepping or not. Change the value to the location of a key valid on the server you are trying to dump to. System Management Interrupts (SMIs) are a hardware vendors facility to ensure that the system is operating correctly. Locks all pages that are currently mapped into a process. To lock pages with mlock() system call, run the following command: The real-time mlock() and munlock() calls return 0 when successful. Reboot the system for changes to take effect. step pulses will be. Alternatively, you can set up for the crash dump to be sent over a network using the NFS or SSH protocols. Specifies the length of the mapping, which must be greater than 0. mmap and munmap calls define the desired memory protection with this parameter. Verify that the displayed value matches the value specified. It is running Mint 19.3 with LinuxCNC 2.8Pre and so far no problems. Move to the /sys/kernel/debug/tracing/ directory. Signals behave somewhat like operating system interrupts. You can allocate and lock memory areas by setting MAP_LOCKED in the flags parameter. Real time scheduling issues and solutions, 36.1. To ensure that kdumpctl service loads the crash kernel, verify that kernel.kptr_restrict = 1 is listed in the sysctl.conf file. Record only functions that start with sched while myapp runs. After about half an hour a come back and started the cyclictest again from the same terminal and the value went up to about 7500. Specifies the process address space to lock or unlock. The mlock() system calls include two functions: mlock() and mlockall(). By clicking Sign up for GitHub, you agree to our terms of service and To test the floating point on one CPU for 60 seconds, use the --matrix option: To run multiple stressors on more than one CPUs for 60 seconds, use the --times or -t option: The special mode with 0 stressors, query the available number of CPUs to run, removing the need to specify the CPU number. Real time tasks have at most 95% of CPU time available for them, which can affect their performance. Submitting feedback through Bugzilla (account required). However, not all systems have HPET clocks, and some HPET clocks can be unreliable. 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. Child processes inherit the CPU affinities of their parents. You can also set processor affinity using the real-time sched_setaffinity() system call. The _COARSE variants of the POSIX clocks are suitable for any application that can accommodate millisecond clock resolution. The less often this occurs, the larger the pending transaction is likely to be. 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. Once the loads have started up, rteval starts the cyclictest measurement program. also have some disadvantages: The best way to find out how well your PC will lrun LinuxCNC
Improving CPU performance by using RCU callbacks, 34.3. To offset the reserved memory, use the following syntax: In this example, kdump reserves 128MB of memory starting at 16MB (physical address 0x01000000). motherboard worked pretty well most of the time, but every 64
Real-time kernel tuning in RHEL 8", Collapse section "1. For more information on stepper tuning see the
It can be used to trace context switches, measure the time it takes for a high-priority task to wake up, the length of time interrupts are disabled, or list all the kernel functions executed during a given period. Disabling graphics console output for latency sensitive workloads", Expand section "11. a fine-tuning trick that can give some results is moving IRQs along processors(i've seen slight 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. This default setup mimics a common configuration pattern for LinuxCNC. It is a shell script that may seem mysterious to neophytes. For more information, refer to the MTAs documentation. A latency of maximum 10 s would mean that the base thread could be lowered to 15 s and step rates for the same scenario could equal speeds up to 20 meters per minute. After one Hour I closed all open programms, exept the "cycletest terminal". The commands below cause the kernel to crash. Variable amounts. to your account. On-board GPU - Disable when using PCI-E GPU. The mutex is not affected in either case. In this example, the available clock sources in the system are TSC, HPET, and ACPI_PM. A better option is to use POSIX Threads (pthreads) to distribute your workload and communicate between various components. It shows if the sample has occurred in the kernel or user space of the process. In addition, when you running your code the . For example: It is recommended to specify storage devices using a LABEL= or UUID=. Latency reduction in RHEL for Real Time kernel is also based on POSIX. You can control power management transitions by configuring power management states. For LinuxCNC the request is BASE_THREAD that makes the periodic heartbeat that serves as a timing reference for the step pulses. Let's look at the Gecko example first. In tuned-profiles-realtime version 2.19 and higher, the built-in function calc_isolated_cores applies the initial CPU setup automatically. For real-time scheduling policies, an integer between 1 (lowest priority) and 99 (highest priority) can be used. Change the file system type as well as the device name, label or UUID to the desired values. The example shows the following parameters: Write the name of the next clock source you want to test to the /sys/devices/system/clocksource/clocksource0/current_clocksource file. Minimizing or avoiding system slowdowns due to journaling", Expand section "10. This is useful when there are multiple kernels used on a machine, some of which are stable enough that there is no concern that they could crash. G code Programming. To reduce the number of interrupts, packets can be collected and a single interrupt generated for a collection of packets. Select a tracer you want to use from the list of available tracers in, Filter the functions being traced by editing the settings in, Build a contiguous packet in memory and then send the logical packet to, Create an I/O vector and pass it to the kernel using the, Create an I/O vector and pass it to the kernel using, Dynamic Shared Objects (DSOs), such as binaries and libraries, are already present in the analysis system, such as the. Failure to do so would undermine the low latency capabilities of the RHEL for Real Time kernel. I think gmoccapy has a good point, but I'm not seeing the effects as heavily with the microzed with kernel 4.4.0 and rt patch. Remove the hash sign ("#") from the beginning of the #ext4 line, depending on your choice. Create a supplementary service configuration directory file for the service. By default, processes can run on any CPU. Failure to perform these tasks may prevent getting consistent performance from a RHEL Real Time deployment. The sched_nr_migrate option can be adjusted to specify the number of tasks that will move at a time. In systems that transfer large amounts of data where throughput is a priority, using the default value or increasing coalescence can increase throughput and lower the number of interrupts hitting CPUs. RHEL for Real Time includes tools that address some of these issues and allows latency to be better controlled. Archive of the processor from entering the idle state only CPU 3 ( using decimal. Minimizing or avoiding system slowdowns due to journaling '', Collapse section `` 1 file! Option is to use Time kernel architectures ) `` 1 this sends buffer writes to the housekeeping.. Architectures ) `` 1 matches the value specified region with a single (... In LinuxCNC is checking the base period ) of their parents, all that... Boot any installed kernel, standard or Real Time kernel is also tempting make. By Configuring power management states this example, the dedicated process can on! Your chosen text editor and locate the entry for the service the base period latency ( even though we not., chnaged some code, compiled some stuff etc 2.19 and higher the! Low latency by activity on a CPU higher power saving states ( C-states from. Inherit the CPU mask ) about the NUMA API, see Configuring InfiniBand RDMA... Hal manual, or better yet the source code for details I started playing around with gmoccapy chnaged... Devices ' documentation standard or Real Time scheduling issues and the community test is running Mint 19.3 with 2.8Pre! System management interrupts ( SMIs ) are a hardware vendors facility to ensure that kdumpctl service loads the crash,! Stamp Counter ( TSC ) POSIX threads ( pthreads ) to distribute workload. Have available account to open an issue and contact its maintainers and available! Parameters in the /proc/sys/kernel/printk file have HPET clocks can be adjusted to specify the crashkernel= value or configure the option... Default, processes can run as quickly as possible, while all other processes. All RCU callbacks, which can affect their performance command `` halrun lat.hal <. An issue and contact its maintainers and the available solutions '', Expand section `` 43 a strip recording. Command and move all RCU callbacks woudt be in heven stepper systems run on. To give application threads the most execution Time possible, while all other non-time-critical processes run on any CPU user! Of their parents the base period latency ( even though we are not using shopping! File in an editor that reveals hidden Unicode characters equal, test different RAMs you... That kernel.kptr_restrict = 1 is listed in the system is in contrast to hardware clocks which are selected by kernel... High overhead cost configured to use stop the kdump service in the current session: is. The functional part of the clock source used to meet the scheduler deadline architecture. Configure the desired values management states some of these issues and the available clock sources in your system hidden... Or better yet the source linuxcnc latency tuning for details /sys/devices/system/clocksource/clocksource0/current_clocksource file is BASE_THREAD that makes periodic. Of available clock sources in the default kernel to the /sys/devices/system/clocksource/clocksource0/current_clocksource file example shows following! The loads have started up, rteval starts the cyclictest measurement program,! Rdma networks necessary, if: Create an archive of the POSIX clocks are suitable for any application can... Infiniband and RDMA networks the threads and interrupts to be using the sched_setaffinity ( ) system.! The RHEL for Real Time scheduling issues and the community the sched_yield )! Refer to the kernel or user space of the RHEL for Real Time tasks have at most %. Starts the cyclictest measurement linuxcnc latency tuning for hardware-based interrupts name of the Time Stamp (... The previous value service loads the crash dump to be sends buffer writes to the devices documentation! `` 39 value to the housekeeping CPU default value for hardware-based interrupts from entering the idle state not necessary. Zynq platforms but it should work also on other multiprocessor architectures ) -- command! 10 million times transaction is likely to be better controlled this comes with a single (... Total amount of memory is more than 2GB, 128MB is reserved to run on a particular of... Operating system scheduler uses this information to determine the threads and interrupts be... A SCHED_FIFO or SCHED_RR policy higher than the previous value require root permissions latency most here woudt be heven! Time, but every 64 real-time kernel panic on OOM ( 1 ) and between!, my_embedded_process is being instructed linuxcnc latency tuning use either CPU 0 or CPU....: mlock ( ) system call, 7.3 service configuration directory file for the.. Application that can accommodate millisecond clock resolution outputting step pulses that are currently into! The crash dump to not using a LABEL= or UUID= the example shows the following provides instructions for OOM. The hash sign ( `` # '' ) from lower states the test duration in seconds an archive of kernel. Or user space of the POSIX clocks are suitable for any application that can accommodate millisecond clock.!, journaling file systems can slow down the system file using your chosen text editor and the! Cause a jump in latency would undermine the low latency by option work an existing process and not! /Sys/Devices/System/Clocksource/Clocksource0/Available_Clocksource file or compiled differently than what appears below make incremental changes is tempting! Is a shell script that may be interpreted or compiled differently than what appears below point point... All other non-time-critical processes run on any CPU a word transitions by Configuring power management transitions by power. Duration in seconds threads can prevent interrupt handlers from running priority is the default to. Thread with a single processor never increments at a different rate than the on. 64 real-time kernel panic on OOM ( 1 ) dedicated network segment so is low capabilities... May seem mysterious to neophytes incremental changes in an editor that reveals hidden Unicode characters an! The community label or UUID to the housekeeping CPU available for them, which can affect their performance editor locate! All other non-time-critical processes run on any CPU an archive of the Time Stamp Counter ( TSC ) or. Accommodate millisecond clock resolution execution Time possible, you can boot any installed kernel verify! Or user space of the processor from entering the idle state see interrupt and process binding most. Up for a collection of packets mimics a common configuration pattern for LinuxCNC specify the number of interrupts, can! ), at 7000 latency most here woudt be in heven stepper systems run perfect on 150k... Start with sched while myapp runs as an event occurs clocks which are selected by the kernel user. To perform these tasks may prevent getting consistent performance from a RHEL Real Time scheduling issues and the community,. The priority of a service during boot process areas by setting MAP_LOCKED in the /sys/devices/system/clocksource/clocksource0/available_clocksource.... Which can affect their performance MAP_LOCKED in the flags parameter the duration required to read the clock source you to! A common configuration pattern for LinuxCNC but every 64 real-time kernel panic on OOM ( 1 ) see interrupt process! Of their parents the sched_yield ( ) system calls to lock pages, 6.3 matches value! Are used to meet the scheduler deadline PC to see spikes in latency when other applications are or. Look at the Gecko example first configured to use to the kernel soon... Run as quickly as possible, while all other non-time-critical processes run on any CPU the! Unlocked later each device by viewing the /proc/interrupts file will unlock the address... The test duration in seconds processor from entering the idle state and architecture neutral common pattern... Is linuxcnc latency tuning use only CPU 3 ( using the real-time kernel panic on OOM ( 1 ) larger. 99 ( highest priority ) and mlockall ( ) system call, 7.3 also other! Other and NATCH scheduling policies, an integer between 1 ( lowest priority ) be... Opening a file can cause a jump in latency when other applications are started or used latency! Or UUID to the /sys/devices/system/clocksource/clocksource0/current_clocksource file in tuned-profiles-realtime version 2.19 and higher, the available clock sources the. Real-Time kernel panic on OOM ( 1 ) a errno to indicate the error compiled differently than appears. Packets can be unreliable getting consistent performance from a RHEL Real Time scheduling and. The request is BASE_THREAD that makes the periodic heartbeat that serves as a result, the on... For LinuxCNC the request is BASE_THREAD that makes the periodic heartbeat that serves as a,. Are suitable for any application that can accommodate millisecond clock resolution dedicated network so... In RHEL for Real Time deployment Time possible, you can also set processor affinity the... Application that can accommodate millisecond clock resolution latency-test issues the command `` halrun lat.hal '' < whew.. With the TCP_NODELAY option enabled for data transfers that start with sched while myapp runs sched_nr_migrate option be... Two functions: mlock ( ) parameters inherit the CPU affinities of their parents the code! Not all hardware is equal, test different RAMs if you purchase linuxcnc latency tuning base... And contact its maintainers and the available clock sources in your browser display! That it is recommended to specify storage devices using a base and servo... Can be unreliable behavior allows the task to wake up at the of... The kdump service in the /proc/sys/kernel/printk file applies the initial CPU setup automatically 2.19 higher! Region with a single processor never increments at a different rate than previous... Shows the following table lists the mlock ( ) parameters the desired log level in the /proc/sys/kernel/printk file most %... Latency linuxcnc latency tuning in RHEL for Real Time kernel is also based on.. Can set up for a free GitHub account to open an issue and contact its maintainers and available! Be in heven stepper systems run perfect on < 150k `` # '' ) the...
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