On Thu, Nov 07, 2019 at 10:32:01PM +0800, shile.zhang@xxxxxxxxxxxxxxxxx wrote: > From: Shile Zhang <shile.zhang@xxxxxxxxxxxxxxxxx> > > Hi, > > I found the unwind_init taken long time (more than 90ms) in kernel > booting, mainly spent on sorting the two ORC unwind tables, orc_unwind > and orc_unwind_ip. > > I also noticed that this issued has reported and discussed last year: > https://lkml.org/lkml/2018/10/8/342 > But seems no final solution until now, I tried to sort the ORC tables at > build time, followed the helpful hints from Josh and Ingo in that thread. > And mainly referred the implementation of 'sortextable' tool: > https://lore.kernel.org/linux-mips/1334872799-14589-1-git-send-email-ddaney.cavm@xxxxxxxxx/ > > What I did: > > - Add a Kconfig to control build-time sorting or runtime sorting; > - Referred 'sortextable', create a similar helper tool 'sortorctable', > help to sort the ORC unwind tables at vmlinux link process. > > One potential improvement is to sort the module ORC tables in future. > > Thanks! Thanks a lot for working on this! I'd say the new config option isn't needed. The runtime ORC sorting logic is unconditionally bad and the code should just be removed. I saw recently that it's one of the main offenders for boot time latency. I also agree with Peter that we should try to reduce the link-time penalty as much as possible. But it's a necessary evil to a certain extent. -- Josh
