On Thu, Aug 22, 2024 at 03:41:08PM -0500, Wei Huang wrote: > Hi All, > > TPH (TLP Processing Hints) is a PCIe feature that allows endpoint > devices to provide optimization hints for requests that target memory > space. These hints, in a format called steering tag (ST), are provided > in the requester's TLP headers and allow the system hardware, including > the Root Complex, to optimize the utilization of platform resources > for the requests. > > Upcoming AMD hardware implement a new Cache Injection feature that > leverages TPH. Cache Injection allows PCIe endpoints to inject I/O > Coherent DMA writes directly into an L2 within the CCX (core complex) > closest to the CPU core that will consume it. This technology is aimed > at applications requiring high performance and low latency, such as > networking and storage applications. Thanks for this example, it's a great intro. Suggest adding something similar to a patch commit log, since the cover letter is harder to find after this appears in git. > This series introduces generic TPH support in Linux, allowing STs to be > retrieved and used by PCIe endpoint drivers as needed. As a > demonstration, it includes an example usage in the Broadcom BNXT driver. > When running on Broadcom NICs with the appropriate firmware, it shows > substantial memory bandwidth savings and better network bandwidth using > real-world benchmarks. This solution is vendor-neutral and implemented > based on industry standards (PCIe Spec and PCI FW Spec). > > V3->V4: > * Rebase on top of the latest pci/next tree (tag: 6.11-rc1) No need to rebase to pci/next; pci/main is where it will be applied. But it currently applies cleanly to either, so no problem. > * Add new API functioins to query/enable/disable TPH support > * Make pcie_tph_set_st() completely independent from pcie_tph_get_cpu_st() > * Rewrite bnxt.c based on new APIs > * Remove documentation for now due to constantly changing API I'd like to see this documentation included. And updated if the API changes, of course. > * Remove pci=notph, but keep pci=nostmode with better flow (Bjorn) This seems backward to me. I think "pci=notph" makes sense as a way to completely disable the TPH feature in case a user trips over a hardware or driver defect. But "pci=nostmode" is advertised as a way to quantify the benefit of Steering Tags, and that seems like it's of interest to developers but not users. So my advice would be to keep "pci=notph" and drop "pci=nostmode". Bjorn
