Windows interrupt latency

Hard pagefaults are events that get triggered by making use of virtual memory that is not resident in RAM but backed by a memory mapped file on disk. The process of resolving the hard pagefault requires reading in the memory from disk while the process is interrupted and blocked from execution. Threats include any threat of suicide, violence, or harm to another. Any content of an adult theme or inappropriate to a community web site. Any image, link, or discussion of nudity. Any behavior that is insulting, rude, vulgar, desecrating, or showing disrespect.

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Any image, link, or discussion related to child pornography, child nudity, or other child abuse or exploitation. So not sure what is causing this error. Using the same core for the interrupt, DPC, and user mode thread exhibits worse performance as load increases because the ISR, DPC, and thread contend for the use of the core.

If you need to achieve the lowest latency, you should request a BIOS version from your hardware provider that reduces SMIs to the lowest degree possible. The operating system cannot control SMIs because the logical processor is running in a special maintenance mode, which prevents operating system intervention. In earlier versions of Windows, the Windows network stack used a fixed-size receive window 65, bytes that limited the overall potential throughput for connections. The total achievable throughput of TCP connections could limit network usage scenarios.

TCP receive window autotuning enables these scenarios to fully use the network. For a TCP receive window that has a particular size, you can use the following equation to calculate the total throughput of a single connection. For example, for a connection that has a latency of 10 ms, the total achievable throughput is only 51 Mbps.

This value is reasonable for a large corporate network infrastructure. However, by using autotuning to adjust the receive window, the connection can achieve the full line rate of a 1-Gbps connection.

Some applications define the size of the TCP receive window. If the application does not define the receive window size, the link speed determines the size as follows:. For example, on a computer that has a 1-Gbps network adapter installed, the window size should be 64 KB. This feature also makes full use of other features to improve network performance. By using these features, Windows-based computers can negotiate TCP receive window sizes that are smaller but are scaled at a defined value, depending on the configuration.

This behavior the sizes easier to handle for networking devices. You may experience an issue in which the network device is not compliant with the TCP window scale option , as defined in RFC and, therefore, doesn't support the scale factor.

In such cases, refer to this KB , Network connectivity fails when you try to use Windows Vista behind a firewall device or contact the Support team for your network device vendor. You can use either netsh commands or Windows PowerShell cmdlets to review or modify the TCP receive window autotuning level. Unlike in versions of Windows that pre-date Windows 10 or Windows Server , you can no longer use the registry to configure the TCP receive window size.

For more information about the deprecated settings, see Deprecated TCP parameters. For detailed information about the available autotuning levels, see Autotuning levels. For more information about this command, see Netsh commands for Interface Transmission Control Protocol.

Software techniques usually rely on storing an accurate time-stamp at the earliest opportunity in an ISR. If you're certain the time between interrupt line becoming asserted and the ISR running is negligible, this might be valid. If, on the other hand, disabling of interrupts is being used to control concurrency, or interrupts are nested, you probably want to be measuring this as well. Stack Overflow for Teams — Collaborate and share knowledge with a private group.

Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. How to test Interrupt Latency? Ask Question. Asked 8 years, 1 month ago. Active 8 years, 1 month ago. Viewed 1k times. Windows Embedded Compact 7. Logically, during the processing of an interrupt, the lower the IRQL drops as processing proceeds from ISR to DPC and then on to user process servicing, the higher and more frequent latency spikes are to be expected.

A common way for a device to indicate that it requires attention from the software is to generate an interrupt. The execution of the ISR can be delayed by various factors. The CPU may be temporarily deferring interrupts, the operating system could be servicing a higher level interrupt, temporarily have its maskable interrupts disabled as a result of some system wide lock state or otherwise. Also, the interrupt may be delayed by hardware factors. Unfortunately it is not possible to measure such interrupt latencies through software alone.

It would require assistance of the hardware or by using a bus analyzer [ In modern Intel architecture systems, we know that this hardware latency is very low, almost always less than one microsecond — Editors ]. In this article, we will only discuss latencies during the software part of interrupt processing, that is, from the moment an ISR started executing until the moment the interrupt got serviced by the software.

As Windows does not allow prioritization control of device interrupts, at any time while an ISR routine is executing it can be preempted by a higher level interrupt unless it takes measures to prevent such preemption by raising IRQL. Latencies during ISR processing can also be introduced by other factors such as the operating system interrupt processing of the system clock, Inter Processor Interrupt IPI routines or even factors beyond the control of the operating system such as System Management Interrupt SMI routines and various hardware factors which will be discussed later.

Generally, the DPC starts executing immediately on the same processor as it was requested on. The operating system maintains a DPC queue per logical processor and it may be possible that other DPC routines will execute first before yours when the DPC queue on your processor is being drained, thus adding latency. And this is where artifacts are most often introduced See sidebar, Play By the Rules , below.

In practice, many drivers are violating this rule, at least when run on certain hardware. Network drivers WiFi in particular , storage port drivers and ACPI battery drivers are among the most notorious for causing high latencies during interrupt processing.

Often such drivers need to be disabled when configuring a system to handle tasks with real-time demands. Executing user-mode code in the request processing path of a real-time solution should generally be avoided.

However there are situations and solutions that require this. As the user-mode code executes in a critical path, obviously that code should execute as quickly as possible. The user-mode code should preferably not block, wait or even call any Windows API library functions at all. It should only make use of resident memory as hard pagefaults can cause long suspensions of execution of a thread while the page fault handler needs to resolve it by synchronously reading in data from disk, which can take seconds.

Note that Windows API functions such as VirtualLock only allow an allocation to be assigned to the working set of a process and do not provide the application with memory which is guaranteed to be resident in RAM. A sure way to provide an application with resident memory is to have a driver lock buffers provided by the user into memory.

There are numerous ways to do this, some more complex than others. The driver then keeps this buffer — with the locked memory — in progress until the application exits.

There are other, more complex, ways of locking shared memory between user-mode and kernel-mode as well. The advantages and disadvantages of each are outside the scope of this article.