PCIe Root flow control credit can't update intime for EP to achieve better performance in Intel Gen4

[Anonymous]

our product is PCIe Gen4 SSD, and when connect to several PCIe gen4 platform, such as  I9-11900K, we find there are strange scenario：

1.  if the host address is PCIe max payload size align(for example，MPS=256， and host memory allocated start address is also 0x100), then our product can achieve better performance when writing data to host memory with pressure test.  

in such scenario, our all MemWr requst is start with address with MPS align, and with MPS length

the PCIe RC return the FC credit in about 40ns interval, so we can achieve 6.4Gbps

2.  if the host address is not PCIe max payload size align(for example，MPS=256， and host memory allocated start address is also 0x010), then our product can not achieve expected performance when writing data to host memory with pressure test.  

in such scenario, our all MemWr requst is start with address (start address will be 0x010 for first MemWr, and next TLP start address will be 0x010+MPS length, and so on), and always with MPS length

the PCIe RC return the FC credit in about 60ns interval, so we can achieve 4.26Gbps

could you help to explain why such scenario, as in PCIe spec, there should no requirement on MemWr start address alignment, so why did above 2 scenario have performance difference?

we didn't see this issue in Gen3 platform. and the AMD gen4 platform also didn't have such issue

[AndrewG_Intel]

Hello Anonymous

Thank you for posting on the Intel® communities.

In order to understand better this request and provide you with the proper information, could you please provide us with more details?

1- Please share more details regarding your product "PCIe Gen4 SSD". Is this a product that is already available in the market? Could you please confirm the maker/manufacturer? Also, is there a model reference number for this "PCIe Gen4 SSD" product and maybe a public link to specifications?

2- More details about the system where you are using your product and the Intel® Core™ i9-11900K Processor. For instance:

• Motherboard/Computer maker and model:
• BIOS version:
• Operating System Version and Build number:

3- Details about any software or tool that you are using to monitor the performance when writing data:

Best regards,

Andrew G.

Intel Customer Support Technician

[AndrewG_Intel]

Hello Anonymous

We are checking this thread and we would like to know if you need further assistance. Please do not hesitate to contact us back if you have additional inquiries.

Best regards,

Andrew G.

Intel Customer Support Technician

[AndrewG_Intel]

Hello Anonymous

We have not heard back from you so we will proceed to close this thread now. If you need any additional information, please submit a new question as this thread will no longer be monitored.

Best regards,

Andrew G.

Intel Customer Support Technician