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Diffstat (limited to 'Documentation/accel/qaic/qaic.rst')
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diff --git a/Documentation/accel/qaic/qaic.rst b/Documentation/accel/qaic/qaic.rst index c88502383136..9ccbfea86f5a 100644 --- a/Documentation/accel/qaic/qaic.rst +++ b/Documentation/accel/qaic/qaic.rst @@ -10,6 +10,9 @@ accelerator products. Interrupts ========== +IRQ Storm Mitigation +-------------------- + While the AIC100 DMA Bridge hardware implements an IRQ storm mitigation mechanism, it is still possible for an IRQ storm to occur. A storm can happen if the workload is particularly quick, and the host is responsive. If the host @@ -35,6 +38,26 @@ generates 100k IRQs per second (per /proc/interrupts) is reduced to roughly 64 IRQs over 5 minutes while keeping the host system stable, and having the same workload throughput performance (within run to run noise variation). +Single MSI Mode +--------------- + +MultiMSI is not well supported on all systems; virtualized ones even less so +(circa 2023). Between hypervisors masking the PCIe MSI capability structure to +large memory requirements for vIOMMUs (required for supporting MultiMSI), it is +useful to be able to fall back to a single MSI when needed. + +To support this fallback, we allow the case where only one MSI is able to be +allocated, and share that one MSI between MHI and the DBCs. The device detects +when only one MSI has been configured and directs the interrupts for the DBCs +to the interrupt normally used for MHI. Unfortunately this means that the +interrupt handlers for every DBC and MHI wake up for every interrupt that +arrives; however, the DBC threaded irq handlers only are started when work to be +done is detected (MHI will always start its threaded handler). + +If the DBC is configured to force MSI interrupts, this can circumvent the +software IRQ storm mitigation mentioned above. Since the MSI is shared it is +never disabled, allowing each new entry to the FIFO to trigger a new interrupt. + Neural Network Control (NNC) Protocol ===================================== |