18.104.22.168. Completion Status Update
There are two modes for selecting the descriptor completion status, MSI-X mode & Writeback mode. The default mode is Writeback. This can be changed, if desired, in the following C header file.
drivers/net/mcdma/rte_pmd_mcdma.h /* Set default descriptor completion */ #define IFC_CONFIG_MCDMA_COMPL_PROC <Set with following method >
Writeback mode: (CONFIG_MCDMA_QUEUE_WB)
In this approach, MCDMA IP updates the completed descriptor index in the host memory. MCDMA PMD goes for local read and not for PCIe read.
MSI-X interrupt mode: (CONFIG_MCDMA_QUEUE_MSIX)
In this approach, when the transaction is completed, the MCDMA IP sends the interrupt to the Host and updates the completed descriptor index in the host memory. MCDMA PMD reads the completion status up on receiving the interrupt.
Register Mode (CONFIG_QDMA_QUEUE_REG)
In this approach, driver knows the completion status by polling the completion head register. As register read is costly from host perspective, performance of smaller payloads would be less in this approach.
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