Re: [PATCH] selftests/net: deflake GRO tests and fix return value and output

On Mon, Feb 24, 2025 at 12:48:30PM -0800, Jakub Kicinski wrote:

With msec-long deferrals we'll flush due to jiffies change. At least
that explains a bit. Could you maybe try lower timeouts than 1msec?
Previously we'd just keep partially-completed packets in GRO for up 
to 1msec, now we'll delay all packet processing for 1msec, that's a lot.

Results again with each test run 1000 times:

gro_flush_timeout=50us  napi_defer_hard_irqs=1 --> failed to GRO 0 times
gro_flush_timeout=100us napi_defer_hard_irqs=1 --> failed to GRO 0 times

gro_flush_timeout=50us  napi_defer_hard_irqs=0 --> failed to GRO 36 times
gro_flush_timeout=100us napi_defer_hard_irqs=0 --> failed to GRO 46 times

100us with 1 defer seems to work fine and is well below the duration of
a jiffy. So we'll usually be testing the "default" GRO path and only
occasionally the jiffy-update path. I'll make these the numbers in the
revised patch unless someone thinks otherwise.