On 12/3/2022 1:51 AM, Eric Pilmore wrote:
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.
Curious why this bug only effected the AMD DMA driver.... It should've
impacted all DMA drivers through NTB right? Did it make any difference
with the ioatdma after the change?
Eric
