cpustat | high frequency performance measurements for Linux This project is deprecated and not maintained | Analytics library

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Disclaimer: following text contains grammar mistakes but i dont give a damn

Maintaining one gigantic slice to hold all data there is is wery costy mainly when it constantly extends. Each time you append few elements, whole memory section is copied to bigges section to allow expansion. with grownig slice, complexity grows and each realocation is slower and slower. You told us that you emulate tousands of cpu states per second.

The best way to deal with this is allocating fixed buffer of some length. Now we now that eventually we will run out of space. When that happens we have two options. First you can write all data ftom buffer to file then truncate the buffer and start filling again (then write again). Other option is to save filled buffers in a slice and allocate new one. Choos witch one fits your machine. (slow or small ram is not good for second solution)

i think this also helps the emulator it self. There will be performance spikes when restoring buffer, but most of the time, performance will be at maximum. Allocating big memory is just slow as alocator is less likely to find fitting section on first try. Garbage collection is also wery unhappy with frequent allocations. By allocating buffer and filling it, we use one big allocation, (but not too big), and store data in sections. Sections we already saved can stey where they are. We can also say that in this case we are handling memory our selfs more then gc does. (no garbage memory produced)

Device emulation (of all devices, not just PCI) under KVM gets handled by the "case KVM_EXIT_IO" (for x86-style IO ports) and "case KVM_EXIT_MMIO" (for memory mapped IO including PCI) in the "switch (run->exit_reason)" inside kvm_cpu_exec(). qemu_wait_io_event() is unrelated.

Want to know how execution gets to "emulate a register read on a PCI device" ? Run QEMU under gdb, set a breakpoint on, say, the register read/write function for the ethernet PCI card you're using, and then when you get dropped into the debugger look at the stack backtrace. (Compile QEMU --enable-debug to get better debug info for this kind of thing.)

PS: If you're examining QEMU internals for educational purposes, you'd be better to use the current code, not a year-old release of it.

The KVM API design requires each virtual CPU in the VM to have an associated userspace thread in the program like QEMU which is controlling that VM (this program is often called a "Virtual Machine Monitor" or VMM, and it doesn't have to be QEMU; other examples are kvmtool and firecracker).

The thread behaves like a normal userspace thread within QEMU up to the point where it makes the KVM_RUN ioctl. At that point the kernel uses that thread to execute guest code on the vCPU associated with the thread. This continues until some condition is encountered which means that guest execution can't proceed any further. (One common condition is "the guest made a memory access to a device that is being emulated by QEMU".) At that point, the kernel stops running guest code on this thread, and instead causes it to return from the KVM_RUN ioctl. The code within QEMU then looks at the return code and so on to find out why it got control back, deals with whatever the situation was, and loops back around to call KVM_RUN again to ask the kernel to continue to run guest code.

Typically when running a VM, you'll see that almost all the time the thread is inside the KVM_RUN ioctl, running real guest code. Occasionally execution will return, QEMU will spend as little time as possible doing whatever it needs to do, and then it loops around and runs guest code again. One way of improving the efficiency of a VM is to try to ensure that the number of these "VM exits" is as low as possible (eg by careful choice of what kind of network or block device the guest is given).

This usagePercent function works by

1. looking at the cycle-count values in os.cpus[index] in the object returned by the os package.
2. delaying the chosen time, probably with setTimeout.
3. looking at the cycle counts again and computing the difference.

You'll get reasonably valid results if you use much shorter time intervals than one second.

Or you can rework the code in the package to do the computation for all cores in step 3 and return an array rather than just one number.

Or you can use Promise.all() to run these tests concurrently.

Siblings in react don't communicate directly, instead they need to communicate via a shared parent, which holds the shared state. You could define an array in the main view state to hold the terminals lines. Then the CPU can push to that array. in the code below i have named this variable terminalLines.

So here's the implementation I did to make it work. (Not sure if it's ideal so please feel free to make any suggestions)

I added "endpoint" to state.projects which holds the data I get from my backend.

Then in my "projects list" component mentioned shown in the question, I pass projects (from state.projects) as props

Add plt.ylim([0, 100]) to animate fix the y limits from 0 to 100 as you say in (1.),

It turned out the real culprit was not FetchM, but other parts of my code that required inlining of a lot of functions (one per each monadic bind in my main CPU monad!), and FetchM just increased the number of binds.

The real problem was that my CPU monad was, among other things, a Writer (Endo CPUOut), and all those CPUOut -> CPUOut functions needed to be fully inlined since CLaSH can't represent functions as signals.

All of this is explained in more detail in the related CLaSH bug ticket.