Resplendence Software - LatencyMon In Depth Latency Tests

In Depth Latency Tests

IDLT (In Depth Latency Tests) is a separate utility that comes installed with LatencyMon. The software allows you to perform several isolated tests to further investigate possible latency problems with a system that's required to perform real-time tasks. These tests cannot run properly while other tests are executing at the same time, which is one of the reasons why we decided to contain them in a separate utility. The tests that IDLT performs may give you a deeper insight in the capabilities of a system of processing data in real-time.

Currently the program offers the following functionality:

Tight Loop Latency Test at HIGH_LEVEL IRQL

The Tight Loop Latency Test runs a tight loop spinning at HIGH_LEVEL interrupt request level and with all maskable interrupts disabled. This is the highest hardware priority level, which means that no hardware device request can interrupt execution. The highest interruption interval of this loop is measured and reported.

This test allows you to measure the duration of System Management Interrupts (SMIs) as the execution of this test can only get interrupted by SMIs, CPU stall or possible CPU problems. Note that SMIs initiated by software will not be measured by this test.

Tight Loop Latency Test at CLOCK_LEVEL IRQL

The Tight Loop Latency Test runs a tight loop spinning at CLOCK_LEVEL interrupt request level. This is a hardware priority level at which all device interrupts are disabled. It means that no hardware device request can interrupt the tight spinning loop test. The highest interruption interval of this loop is measured and reported. This test can only get interrupted by Inter Processor Interrupts (IPIs), System Management Interrupts (SMIs), CPU stalls or a CPU problem. Note that most SMIs initiated by software will not be measured by this test.

Tight Loop Latency Test at DISPATCH_LEVEL IRQL

The Tight Loop Latency Test runs a tight loop spinning at DISPATCH_LEVEL interrupt request level. This is a hardware priority level at which all device interrupts are enabled. Code running at this level cannot get preempted by other threads running in the system, nor can it get interrupted by DPCs. Hardware device request instead can interrupt code running at DISPATCH_LEVEL. The highest interruption interval of this loop is measured and reported.

This test allows you to measure the durations of all sorts of device and hardware interrupts including ISRs (Interrupt Service Routines), IPIs (Inter-processor interrupts), SMIs (System Management Interrupts) and CPU stalls but not DPCs (Deferred Procedure Calls).