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Kernelshark download windows
Thinking more about this case, one must think about what would cause a high priority task to wake up in the first place. If it is woken up periodically to do some work, then it can very well be the case that it will be cache cold. Any task that was scheduled in between can easily push out the cache of this high priority task. But what if the high priority task was blocked on a mutex? If the task was blocked on a mutex and another RT task was scheduled in its place then when the high priority task wakes up again, there is a good chance that the task will be cache hot.
A mutex in most real-time programs will usually be held for a short period of time. Migrating a task simply because it blocked on a mutex increases the impact these locks have on the throughput.
Why punish the high priority task even more because it blocked and had to wait for another task to run? Before making any decision to change the code, I needed to have a test case that can show that the moving of a high priority task instead of preempting the lower priority task will cause the high priority task to ping pong around the CPUs when there is lock contention. A high priority task should not be punished migrated if it simply encounters lock contention with lower priority real-time tasks.
It would also be helpful to know how changing this decision affects the total number of migrations for all the tasks under lock contention. First try Having a 4 processor box to play with, I started writing a test case that would possibly cause this scenario, and use Ftrace to analyze the result. The first test case to try was to create five threads one more than CPUs and four pthread mutex locks. Have all threads wake up from a barrier wait and then loop 50 times grabbing each lock in sequence and do a small busy loop.
The name of this test is called migrate. You can specify another file by naming it as the first argument to KernelShark. While the KernelShark display images may be difficult to read fully in the article, clicking any of them will bring up a full-resolution version.
Since all tasks have been recorded, even trace-cmd itself, we want to filter out any tasks that we do not care about. In the default graph view, each on-line CPU is represented by a plot line. Each task is represented by a different color. The color is determined by running the process ID through a hash function and then parsing that number into a RGB format.
The lines sticking out of the top of the bars represent events that appear in the list below the graph. By examining the graph we can see that the test case was quite naive.
The lowest priority task, thread 0, never got to run until the other four tasks were finished. This makes sense as the machine only had four CPUs and there were four higher priority tasks running.
The four running tasks were running in lock step, taking the locks in sequence. From this view it looks like the tasks went out of sequence, but if we zoom in to where the migrations happened, we see something different. To zoom into the graph, press and hold the left mouse button. A line will appear, then drag the mouse to the right. As the mouse moves off the line, another line will appear that follows the mouse.
When you let go of the mouse button, the view will zoom in making the locations of the two lines the width of the new window. Repeating the above procedure, we can get down to the details of the migration of thread 3. Double clicking on the graph brings the list view to the event that was clicked on.
A green line appears at the location of that was clicked. Because we filtered out all threads but the migration test tasks, we see a small blank on the CPU 0 line. The priority shown is represented by the kernel’s view of priority, which is inverse to what user-space uses user space priority 99 is kernel priority zero.
Zooming into the other migrations that happened on the other CPUs, show that the watchdog kernel thread was responsible for them as well. If it wasn’t for the watchdog kernel threads, this test would not have had any migrations. The first test took the naive approach of just setting up four locks and having the tasks grab them in order.
But this just kept the tasks in sync. The next approach is to try to mix things up a little more. The concern about the real-time scheduler is how it affects the highest priority task. The next test creates the four locks again as there are four CPUs and five tasks each of increasing priority. This time, only the highest priority task grabs all the locks in sequence. The other four tasks will grab a single lock. Each lock will have a single task and the highest priority task grabbing that lock.
To try to force contention, pthread barriers are used. For those unfamiliar with pthread barriers, they are synchronization methods to serialize threads.
A barrier is first initialized with a number and all threads that hit the barrier will block until that number of threads have hit the barrier, then all the threads are released. The high priority task will hit that barrier before it takes the corresponding lock. Because the low priority task is already waiting on the barrier, the high priority task will trigger the barrier to release both tasks because the barrier has a task limit of two.
The high priority task will most likely try to take the mutex while the low priority task aleady has it. Running this test under trace-cmd yields the following from KernelShark after filtering out all but the migrate test tasks. As the colors of the tasks are determined by their process IDs, this run has the following: The initial green bar is the main thread that is setting up all the locks and barriers.
The light purple bar is the lowest priority thread 0. The red bar is the next-higher priority thread 1. The yellow ish bar is the next-higher priority thread 2. The blue bar is the next-higher priority thread 3. The light turquoise bar is the highest priority thread 4. Looking at the graph it seems that the highest priority thread stayed on the same CPU, and was not affected by the contention.
Considering that the scheduler is set to migrate a waking real-time task if it is woken on a CPU that is running another real-time task, regardless of the priorities, one would think the high priority task would have migrated a bit more.
Zooming in on the graph brings to light a bit more details to what is occurring. What we can see from the graph, and from the list, is that the high priority thread did have contention on the lock. But because all threads are waiting for the high priority process to come around to its lock, the other threads are sleeping when the high priority process wakes up. The high priority process is only contending with a single thread at a time.
The second test was on the right track. It was able to produce a contention but failed to have the CPUs busy enough to cause the highest priority task to wake up on a CPU running another real-time task.
What is needed is to have more tasks. Compressed tar package: shark The disk contains also a RAM disk tool. For linux user: unzip fdremote. Back to quick links Online S. Repository The download directory contains all the available tools for S.
The main S. Repository contains the complete S. The S. Modules Repository contains all the scheduling algorithms and resource sharing policies available for S. The supported applications consist of demo applications regularly updated to the new kernel version by the maintaince team. The unsupported software include unsupported applications and advanced unsupported applications consisting of demo applications developed by users and made available by the maintainance team.
To check out and compile a S. A readme is also provided. Take a look to the CiberMouse competition homepage for more information. For any question, please contact Paulo Pedreiras. Back to quick links. Download Quick links Last Release. Version 1.
Kernelshark download windows
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February 2, The last LWN article on Ftrace described trace-cmdwhich is a front end tool to interface with Ftrace. But reading the output in a text format may be a bit overwhelming, and make it hard to see the bigger picture. To be able to understand how processes interact, a GUI can help humans see what is happening at a global scale. KernelShark has been written to fulfill this requirement. It is a GUI front end to trace-cmd. These two tools have been kept separate since a lot of embedded kernelshark download windows do not have the libraries needed to build KernelShark.
After installing the documentation, you can access the help directly from KernelShark kernelshark download windows the “Help” menu. This article is not a tutorial on using KernelShark, as everything you need to know about the tool is kept up-to-date in the KernelShark repository.
Instead, this article will describe a use case that KernelShark was instrumental in helping to solve. One would think that the proper thing to do would be to simply wake up the high priority process on that CPU which would cause the lower priority process to be pushed off the running CPU. But a theory was that by doing so, we move a cache hot real-time process onto a cache cold CPU and possibly kernelshark download windows it with a cache cold process.
After some debate, the decision was made to migrate the high priority process to the CPU running the lowest priority task or no task at all and wake it there. Some time later, after the code was incorporated into mainline, I started to question this decision even though I was the one that fought for it.
With the introduction of Ftrace, we now have a utility to truly examine the impact that decision has made. The decision to move the higher priority task was based on an assumption that if the task was waking up, that it is more likely to be cache cold than a task that is already running.
Thinking more about this case, one must think about kernelshark download windows would cause a high priority task to wake up in the first place. If it is woken up periodically to do some kernelshark download windows, then it can very well be the case that it will be cache cold. Any task that was scheduled in between can kernelshark download windows push out the cache of this high priority task.
But what if the high kernelshark download windows task was blocked on a mutex? If the task was blocked on a mutex and another RT task was scheduled in its place then when the high priority task wakes up again, there is a kernelshark download windows chance that the task will be cache hot. A mutex in most real-time programs will usually be held for a short period of time.
Migrating a task kernelshark download windows because it blocked on a mutex increases the impact these locks have on the throughput. Why punish the high priority task even more because it blocked and had to wait for another task to run? Before kernelshark download windows any decision to change the code, I needed to have a test case that can show that the moving of a high priority task instead of preempting the lower priority task will cause the high priority task to ping pong around the CPUs when there is lock contention.
A high priority task should not be punished migrated if it simply encounters вот ссылка contention kernelshark download windows lower priority real-time tasks. Kernelshark download windows would also be helpful to know how changing this decision affects the total number kernelshark download windows migrations for all the tasks under lock contention.
First try Having a 4 processor box to play with, I started writing a test case that would possibly cause this scenario, and use Ftrace to analyze the result.
The first test case to try was to create five threads one more than CPUs and four pthread mutex locks.
Have all threads http://replace.me/28909.txt up from a barrier wait and then loop 50 times grabbing each lock in sequence and do a small busy loop. Перейти на страницу name of this test is called migrate. You can specify another file by naming it as the first argument to KernelShark. While the KernelShark display images may be difficult to read fully in the article, clicking any of them will bring up a full-resolution version.
Since all tasks have been recorded, even trace-cmd itself, we want to filter out any tasks that we do not care about. In the default graph view, each on-line CPU is represented by a plot line.
Each task is represented by a different color. The color is determined by running the перейти ID through a hash function and then parsing that number into a RGB format. The lines sticking out of the top of the bars represent events that appear in the list below the graph.
By examining the graph we can see that the test case was quite naive. The lowest priority task, thread 0, never got to run until the other four tasks were finished. This makes sense as the machine only had four CPUs and there were four higher priority tasks running. The four running tasks were running kernelshark download windows lock step, taking the locks in sequence. From this view it looks like the tasks went out of sequence, but if we zoom in to where the migrations happened, we see something different.
To zoom into the graph, press and hold the left mouse button. A line will appear, then drag the mouse to the kernelshark download windows. As the mouse moves off the line, another line will appear that follows the mouse.
When you let go of the mouse button, the view will zoom in making the locations of the two lines the width of the new window. Repeating the above procedure, we can get down to the details of the migration of thread 3. Double clicking on the graph brings the list view to the event that was clicked on. A green line appears at the location of that was clicked. Because we filtered out all threads but the migration test tasks, we see правы.
windows live messenger facebook chat download этим small blank on the CPU 0 line. The priority shown is represented by kernelshark download windows kernel’s view of priority, which is inverse to what user-space uses user space kernelshark download windows 99 kernelshark download windows kernel priority zero. Zooming into the other migrations that happened on the other CPUs, show that the watchdog kernel thread was responsible for them as well.
If it wasn’t for the watchdog смотрите подробнее threads, this test would not have had any migrations. The first test took the naive approach of just setting up four locks and having the tasks grab them in order. But this just kept the tasks in sync. The next approach is to try to mix things up a little more. The concern about the real-time scheduler is how it affects the highest priority task. The next test creates the four locks again as there are four CPUs and five tasks each of increasing priority.
This time, only the highest priority task grabs kernelshark download windows the locks in sequence. The other жмите tasks will grab a single lock. Each lock will have a kernelshark download windows task and the highest priority task grabbing that lock.
To try to force contention, pthread barriers are used. Kernelshark download windows those unfamiliar with pthread barriers, they are synchronization methods to serialize threads.
A barrier is first initialized with a number and all threads that hit the barrier will block until that number of threads have hit the barrier, then all the threads are released.
The high priority task will hit that barrier before it takes the corresponding lock. Because the low priority task is already waiting on the barrier, the high priority task will kernelshark download windows the barrier to release both tasks because the barrier has a task limit of two.
The high priority task will most likely try to take the kernelshark download windows while the low priority task aleady has it. Running this test under trace-cmd yields the following from KernelShark after filtering out all but the migrate test tasks. As the colors of the tasks are determined by their process IDs, this run has the following: The initial green bar is the main thread that is setting up all the locks and barriers.
The light purple bar is the lowest priority thread 0. The red bar is the next-higher priority thread 1. The yellow ish bar is the next-higher priority thread 2. The blue bar is the next-higher priority thread 3.
The light turquoise bar is the kernelshark download windows priority thread 4. Looking at the graph it seems that the highest kernelshark download windows thread stayed on the same CPU, and was not affected by the contention. Considering that the scheduler is set to migrate a waking real-time task if it is woken on a CPU that is running another real-time task, regardless of the priorities, one would think the kernelshark download windows priority task would have migrated a bit more.
Zooming in on the graph brings to light a kernelshark download windows more details to what is occurring. What we can see from the graph, and from the list, is that the high priority thread did have contention on the lock. But because all threads are waiting for the high priority process to come around to its lock, the other threads are sleeping when the high priority process wakes up.
The high priority process kernelshark download windows only contending with a single thread at a time. The second test was on kernelshark download windows right track.
It was able to produce a contention but failed to have the CPUs busy enough to cause the highest priority task to wake up on a CPU running another real-time task. What is needed is to have kernelshark download windows tasks.
The final test adds twice as many running threads as there are CPUs. This test смотрите подробнее back to all tasks grabbing all locks in sequence. To prevent the synchronization that has happened before, each thread will hold a lock a different amount of time.
The higher the priority of a thread, the shorter time it will hold the lock. Not only that, but the threads will now sleep after they release a lock. When a higher priority thread blocks on a mutex held by a lower priority thread, the lower priority thread will inherit the priority of the thread it blocks.
The test records the kernelshark download windows of times each task voluntarily schedules, the number of times it is preempted, the number of times kernelshark download windows migrates, and the number of times it successfully acquired all locks.
When the test finishes, it gives an output of these for each thread. The higher the task number the higher the priority of the thread it kernelshark download windows.
Running this test under trace-cmd and viewing it with KernelShark yields a graph with lots of pretty colors, which means we kernelshark download windows succeeded in our goal. To prove kernelshark download windows the highest priority thread did indeed migrate, we can plot the thread itself. Using the “Plots” menu and choosing “Tasks” brings up the same type of dialog as the task filter that was described earlier. I selected the highest priority thread migrateand zoomed in to get a better view.
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