Hi, Arnd, On Tue, Feb 7, 2023 at 10:11 PM Arnd Bergmann <arnd@xxxxxxxx> wrote: > > On Tue, Feb 7, 2023, at 14:28, Jianmin Lv wrote: > > On 2023/2/7 下午6:32, Arnd Bergmann wrote: > >> I agree the default should always be to have a kernel that works on > >> every machine that has been produced, but this also depends on which > >> models specifically lack the unaligned access. If it's just about > >> pre-production silicon that is now all but scrapped, things are different > >> from a situation where users may actually use them for normal workloads. > >> > >> Is there an overview of the available loongarch CPU cores that have > >> been produced so far, and which ones support unaligned access? > > > > So far, produced CPUs based LoongArch include 3A5000, 3B5000, 3C5000L, > > 3C5000, 2K2000, 2K1000LA and 2K0500, where 2K1000LA and 2K0500 are > > unaligned-access-unsupported, and others are unaligned-access-supported. > > Ok, so these are actually some of the newer (though low-end) > implementations that require the workaround, not the older chips. > > In this case, I think both the kernel and toolchain need to default > to -mstrict-align, unless someone specifically asks for the variant > that can support unaligned access. The kernel option could be > guarded by 'depends on EXPERT' to ensure that this is not set by > default. > > To be sure that this is set correctly, the > arch/loongarch/kernel/unaligned.c file should also never be included > when EFFICIENT_UNALIGNED_ACCESS is set, to ensure that any attempt > to run such a non-portable kernel on 2K1000LA results in a > a kernel panic rather than silently fixing up the unaligned accesses > at a huge performance cost. OK, sounds reasonable, I will send V2 for that. Huacai > > Arnd >
