On Thu, Oct 15, 2020 at 10:49:17AM +0000, Juraj Linkeš wrote: > Hi dpdk devs, > > Is there a constraint on how low RTE_MAX_LCORE can be? I'm implementing a > discovery mechanism that sets RTE_MAX_LCORE according to the number of > host cores, but I'm hitting errors when the values are low: > https://travis-ci.com/github/jlinkes/dpdk/jobs/399596828 Message: Found 2 > cores Message: Found 1 numa nodes > > ../app/test/test_rcu_qsbr.c:296:54: error: iteration 2 invokes undefined > behavior [-Werror=aggressive-loop-optimizations] > > ../app/test/test_rcu_qsbr.c:315:55: error: array subscript is above array > bounds [-Werror=array-bounds] > > All VM jobs failed in that Travis build. Travis VMs only have 2 cores, so > I tried to put a bound on the build. I set it to 4 and all jobs except > GCC shared lib jobs passed, which still threw iteration 4 invokes > undefined behavior error: > https://travis-ci.com/github/jlinkes/dpdk/jobs/400004089 > > ../examples/performance-thread/l3fwd-thread/main.c:2338:34: error: > iteration 4 invokes undefined behavior > [-Werror=aggressive-loop-optimizations] > > This happens for number of cores < 32 and looks like a limitation unique > to l3fwd (with cores between 4 and 32 - I didn't see the error > elsewhere). > > Should I use the bound or are these legitimate errors? The fact that only > GCC (and not clang) shared lib jobs failed is also suspicious. > Four seems a reasonable lower bound to have, but 32 seems high. I agree that the warning itself looks suspicious too.
However, looking at the code and the line in question, I think there is indeed an app bug. The loop goes up to MAX_ETHPORTS, but the tx_bufs array being dereferenced is dimensioned by MAX_LCORES, which is why you hit problems with lcore values below 32 (==MAX_ETHPORTS). Based on the use, I suspect the structure definition may be wrong and the array should be dimensioned for MAX_ETHPORTS - but I haven't dug into the code further than that. Regards, /Bruce
