> > 10/07/2025 16:37, Andre Muezerie: > > On Tue, Jul 01, 2025 at 04:17:20PM +0200, Thomas Monjalon wrote: > > > 23/05/2025 01:37, Andre Muezerie: > > > > The functions rte_rcu_qsbr_dq_create and rte_rcu_qsbr_dq_reclaim > > > > establish > > > > no limit on the size of each element in the defer queue. > > > > > > Very good, we need more unlimited API in DPDK. > > > > > > > With DPDK 25.11 a hard limit will be set (``RTE_QSBR_ESIZE_MAX``). > > > > > > I think it is a step in the wrong direction. > > > I prefer having no limit. > > > > > > > This will allow fixed C arrays to be used in the functions' > > > > implementations, > > > > avoiding VLAs and use of alloca(). > > > > > > I don't understand this justification. > > > Why trying to remove the 2 alloca() in the lib RCU? > > > > > > > Only because other developer expressed concerns that using alloca() allows > > ill-intended callers to cause a stack overflow. > > I personally also prefer to have no hardcoded limits. > > Yes I vote for keeping alloca(). >
Probably it was me who expressed some concerns, sorry for late reply. I can only repeat what I already replied to David: For that particular case, my reasons are mostly conceptual: using alloca() doesn't really differ from simply using VLA, in fact it makes code looks uglier. I understand that we do want MSVC enabled, and in many cases such mechanical replacement is ok, but probably better to avoid it whenever possible. suppose we have 3 options: 1) use predefined max value (it could be quite big to fit any reasonable usage, let say 1KB or so). 2) use alloca(). 3) come-up with some smarter approach. For 3) - I don't have any good ideas. One option would be to create that ring RING_F_MP_HTS_ENQ flags, then we can use peek API for enqueue part too (rte_ring_enqueue_bulk_elem_start). That would solve an issue, as in that case we wouldn't need to make temp copy of data on the stack. My preference would be either 1) or 3), but I could leave with 2) too - specially that I don't really use that part of RCU lib. Would be really good to hear opinion of RCU lib maintainer. Konstantin
