> >> 'mbufs' is temporarily storage for allocated mbuf pointers, why not > >> allocate if from stack instead, can be faster and easier to manage: > >> "struct rte_mbuf *mbufs[count]" > > > > That would introduce a variable length array. > > VLA's should be removed, they are not supported on Windows and many > > security tools flag them. The problem is that it makes the code > > brittle if count gets huge. > > > > But certainly regular calloc() or alloca() would work here. > > > > Most of the existing bulk alloc already uses VLA but I can see the problem it > is not > being supported by Windows. > > As this mbuf pointer array is short lived within the function, and being in > the fast > path, I think continuous alloc and free can be prevented, > > one option can be to define a fixed size, big enough, array which requires > additional loop for the cases 'count' size is bigger than array size, > > or an array can be allocated by driver init in device specific data ,as we > know it > will be required continuously in the datapath, and it can be freed during > device > close()/uninit(). > > I think an fixed size array from stack is easier and can be preferred.
I sent a v3 of the patch, still using alloc(). I found two problems with using a fixed array: 1. the array size needs to be determined in advance. I don't know what a good number should be. If too big, some of them may be wasted. (and maybe make a bigger mess of CPU cache) If too small, it ends up doing multiple allocations, which is the problem this patch trying to solve. 2. if makes the code slightly more complex ,but I think 1 is the main problem. I think another approach is to use VLA by default, but for Windows use alloc(). Long
