On 21/02/17 11:30, Coly Li wrote: > On 2017/2/21 上午2:14, Wols Lists wrote: >> On 20/02/17 08:07, Coly Li wrote: >>> For the function pointer asignment, it is because I see a brach happens in a loop. If I use a function pointer, I can avoid redundant brach inside the loop. raid1_read_request() and raid1_write_request() are not simple functions, I don't know whether gcc may make them inline or not, so I am on the way to check the disassembled code.. >> >> Can you force gcc to inline or compile a function? Isn't it dangerous to >> rely on default behaviour and assume it won't change when the compiler >> is upgraded? > > I choose to trust compiler, and trust the people behind gcc. > I admire your faith. I seem to remember several occasions where the gcc people added new optimisations and caused all sorts of subtle havoc with the kernel where it relied on the old behaviour. Don't forget - the linux kernel is one of the compiler's most demanding customers. And don't forget also - there are quite a few people now using llvm to compile the kernel (it may not yet be working - I think it is certainly for simple use cases) so tests on gcc don't guarantee it'll work for everyone ... I think you can trace the addition of many kernel compile-time flags to that sort of thing - disabling new optimisations. Cheers, Wol -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
