Maximum payload size vs. Maximum Read Request Size

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Maximum payload size vs. Maximum Read Request Size


PCIe specification defines Maximum Payload Size (MPS) in Rev 3.1 Sec 2.2.2 TLPs with Data Payloads – Rules as a limiter on the TLP size.

Maximum Read Request Size (MRS) is the application layer size of a data that can be transferred at a given time. MRS value needs to be a multiple of MPS and MRS request is sent in chunks of data with MPS size.

Endpoints typically support 4k MRS size.
Linux is currently matching MPS and MRS value. This is causing HW resources to be inefficiently used.



Presentation Materials



  • Biography

    Sinan Kaya is a Linux kernel developer at Qualcomm Datacenter Technologies (QDT). Sinan earned 15 years of embedded systems and real time operating systems experience before joining QDT as a kernel developer in 2013.

    He has been an active kernel contributor since 2015. His main kernel contributions are in PCIe, ACPI and DMA Engine areas.

    He seeks feedback and looks for ways to make Linux standards compliant.