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

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Date:	Fri, 30 May 2014 14:23:04 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Minchan Kim <minchan@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>, "H. Peter Anvin" <hpa@...or.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC 2/2] x86_64: expand kernel stack to 16K

Linus Torvalds <torvalds@...ux-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@...ux.intel.com -- Speaking for myself only
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