Performance Tip: Completing Requests During HwStartIo

By completing outstanding I/O requests that are ready for completion in its HwStorStartIo routine, a miniport can spend less time at device IRQL (DIRQL), which improves system responsiveness, and also take advantage of new Storport optimizations that further improve system responsiveness and I/O throughput. The point is to try to spend as little time as possible in an interrupt handler. To take advantage of the new Storport optimizations, a miniport:

• Must enable DPC redirection via StorPortInitializePerfOpts

• Must use StorPortNotification (NotificationType = RequestComplete) while in its HwStorStartIo routine to notify Storport of completed I/O requests

• Should indicate its intention to do completion-during-StartIo by setting the STOR_PERF_OPTIMIZE_FOR_COMPLETION_DURING_STARTIO flag in its call to the StorPortInitializePerfOpts routine

• Must determine the characteristics of the workload (for example, request size and throughput) that should be present before the optimization is applied.

While in its HwStorStartIo routine, a miniport should check for completed requests after starting the requested I/O operation.

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Build date: 4/17/2013