Hello Jakub,
On Thu, Jul 10, 2025 at 06:45:35PM -0700, Jakub Kicinski wrote:
> > +MAX_WRITES: int = 40
>
> FWIW the test takes 25sec on our debug-heavy VMs right now.
> I think we can crank the writes quite a bit.. ?
Sure. I will increase it to 40. On my VMs I get more than 30 hits every
single time:
2025-07-11 08:30:08,904 - DEBUG - BPFtrace output: {'hits': 30}
2025-07-11 08:30:08,904 - DEBUG - MAPS coming from bpftrace = {'hits':
30}
> > +def ethtool_read_rx_tx_queue(interface_name: str) -> tuple[int, int]:
> > + """
> > + Read the number of RX and TX queues using ethtool. This will be used
> > + to restore it after the test
> > + """
> > + rx_queue = 0
> > + tx_queue = 0
> > +
> > + try:
> > + ethtool_result = ethtool(f"-g {interface_name}").stdout
>
> json=True please and you'll get a dict, on CLI you can try:
>
> ethtool --json -g eth0
Sure. I was parsing manually because some options do not have --json
format.
ethtool --json -l eth0
ethtool: bad command line argument(s)
I haven't checked upstream, but, if this feature is upstream, is it worth
implementing it?
> > + ethtool(f"-G {interface_name} rx {rx_val} tx {tx_val}")
>
> This is setting _ring size_ not queue count.
> I suppose we want both, this and queue count to 1 (with ethtool -l / -L)
> The ring size of 1 is unlikely to work on real devices.
> I'd try setting it to 128 and 256 and if neither sticks just carry on
> with whatever was there.
Thanks. I creating a function to do it. Something as:
def configure_network(ifname: str) -> None:
"""Configure ring size and queue numbers"""
# Set defined queues to 1 to force congestion
prev_queues = ethtool_get_queues_cnt(ifname)
logging.debug("RX/TX/combined queues: %s", prev_queues)
# Only set the queues to 1 if they exists in the device. I.e, they are
> 0
ethtool_set_queues_cnt(ifname, tuple(1 if x > 0 else x for x in
prev_queues))
defer(ethtool_set_queues_cnt, ifname, prev_queues)
# Try to set the ring size to some low value.
# Do not fail if the hardware do not accepted desired values
prev_ring_size = ethtool_get_ringsize(ifname)
for size in [(1, 1), (128, 128), (256, 256)]:
if ethtool_set_ringsize(ifname, size):
# hardware accepted the desired ringsize
logging.debug("Set RX/TX ringsize to: %s from %s", size,
prev_ring_size)
break
defer(ethtool_set_ringsize, ifname, prev_ring_size)
> > + "remote_ip": (
> > + cfg.remote_addr_v["4"] if cfg.addr_ipver == "4" else
> > cfg.remote_addr_v["6"]
> > + ),
>
> this is already done for you
> cfg.addr is either v4 or v6 depending on what was provided in the env
Ack!
> > +# toggle the interface up and down, to cause some congestion
>
> Let's not do this, you're missing disruptive annotation and for many
> drivers NAPI is stopped before queues
> https://github.com/linux-netdev/nipa/wiki/Guidance-for-test-authors#ksft_disruptive
Sure. This is not needed to reproduce the issue.
I just put it in there in order to create more entropy. Anyway, removing
it.
> > +def main() -> None:
> > + """Main function to run the test"""
> > + netcons_load_module()
> > + test_check_dependencies()
> > + with NetDrvEpEnv(__file__, nsim_test=True) as cfg:
>
> I think nsim_test=True will make the test run _only_ on netdevsim.
> But there's nothing netdevsim specific here right?
> You can remove the argument and let's have this run against real
> drivers, too?
Sure. that is our goal, by the end of the day. Being able to run it on
real hardware.
Thanks of the review. I will send an updated version soon, and we can
continue the discusion over there.
--breno
