On Fri, Dec 2, 2022 at 1:57 PM Eric Pilmore <epilmore@xxxxxxxxxx> wrote: > > Was curious if anybody has any expected performance numbers for the > AMD DMA engine "ptdma"? > > I'm doing some testing utilizing the "ntb_netdev" module for TCP/IP > communication between servers via NTB (Non-Transparent Bridge) using > "iperf". I find that on Intel based boxes, utilizing IOAT DMA, I can > get approximately 19-20 Gb/s for a simple untuned single iperf > instance. However, when running on AMD based boxes (Milan CPUs), and > running the latest ptdma driver from the Linux tree, I can only > achieve about 2-3 Gb/s. I'm thinking there must be some driver knob > that I need to tweek or something. > > Any help is greatly appreciated. > > Thanks, > Eric You can disregard this question. The issue turned out to be a bug in the ntb_netdev module. The module was calling dev_kfree_skb() in an inappropriate place (interrupt context). Once that was fixed (changed to dev_kfree_skb_irq()), some assert WARNINGS (that I had previously missed) went away and the performance is as expected. Eric
