<snip> > > On Fri, Apr 30, 2021 at 5:27 PM fengchengwen > <fengcheng...@huawei.com> wrote: > > > > Hi, ALL > > We have a question for your help: > > 1. We have two platforms, both of which are ARM64, one of which > supports > > both NEON and SVE, the other only support NEON. > > 2. We want to run on both platforms with a single binary file, and use the > > highest vector capability of the corresponding platform whenever > possible. > > I see VPP has a similar feature. IMO, it is not present in DPDK. > Basically, In order to do this. > - Compile slow-path code(90% of DPDK) with minimal CPU instruction set > support > - Have fastpath function compile with different CPU instruction set levels -In > slowpath, Attach the fastpath function pointer-based on CPU instruction- > level support. Agree.
> > > > 3. So we build the DPDK program with -march=armv8-a+sve+crc (GCC > 10.2). This defines the minimum capabilities of the target machine. > > However, it is found that invalid instructions occur when the program > > runs on a machine that does not support SVE (pls see below). > > 4. The problem is caused by the introduction of SVE in GCC automatic > vector > > optimization. > > > > So Is there a way to disable GCC automatic vector optimization or use only > > NEON to perform automatic vector optimization? I do not think this is safe. Once SVE is enabled, compiler is allowed to use the SVE instructions wherever it finds it fit. > > > > BTW: we already test -fno-tree-vectorize (as link below) but found no > effect. > > > > https://stackoverflow.com/questions/7778174/how-can-i-disable-vectoriz > > ation-while-using-gcc > > > > > > The GDB output: > > EAL: Detected 128 lcore(s) > > EAL: Detected 4 NUMA nodes > > Option -w, --pci-whitelist is deprecated, use -a, --allow option > > instead > > > > Program received signal SIGILL, Illegal instruction. > > 0x0000000000671b88 in eal_adjust_config () > > (gdb) > > (gdb) where > > #0 0x0000000000671b88 in eal_adjust_config () > > #1 0x0000000000682840 in rte_eal_init () > > #2 0x000000000051c870 in main () > > (gdb) > > > > The disassembly output of eal_adjust_config: > > 671b7c: f8237a81 str x1, [x20, x3, lsl #3] > > 671b80: f110001f cmp x0, #0x400 > > 671b84: 54ffff21 b.ne 671b68 <eal_adjust_config+0x1f4> > > // > b.any > > 671b88: 043357f5 addvl x21, x19, #-1 > > 671b8c: 043457e1 addvl x1, x20, #-1 > > 671b90: 910562b5 add x21, x21, #0x158 > > 671b94: 04e0e3e0 cntd x0 > > 671b98: 914012b5 add x21, x21, #0x4, lsl #12 > > 671b9c: 52800218 mov w24, #0x10 > > // #16 > > 671ba0: 25d8e3e1 ptrue p1.d > > 671ba4: 25f80fe0 whilelo p0.d, wzr, w24 > > 671ba8: a5e04020 ld1d {z0.d}, p0/z, [x1, x0, lsl #3] > > > > > > Best regards. > >
