Re: [RFC 2/2] x86_64: expand kernel stack to 16K

Andi Kleen
2014-05-30T21:23:09Z

Linus Torvalds <torvalds@linux-foundation.org> writes:

> From a quick glance at the frame usage, some of it seems to be gcc
> being rather bad at stack allocation, but lots of it is just nasty
> spilling around the disgusting call-sites with tons or arguments. A
> _lot_ of the stack slots are marked as "%sfp" (which is gcc'ese for
> "spill frame pointer", afaik).

> Avoiding some inlining, and using a single flag value rather than the
> collection of "bool"s would probably help. But nothing really
> trivially obvious stands out.

One thing that may be worth playing around with gcc's
--param large-stack-frame and --param large-stack-frame-growth

This tells the inliner when to stop inlining when too much
stack would be used.

We use conserve stack I believe. So perhaps smaller values than 100
and 400 would make sense to try.

-fconserve-stack
Attempt to minimize stack usage. The compiler attempts to
use less stack space, even if that makes the program slower.
This option
implies setting the large-stack-frame parameter to 100 and
the large-stack-frame-growth parameter to 400.

-Andi

--
ak@linux.intel.com -- Speaking for myself only