linux-kernel - Re: new execve/kernel

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Date:	Fri, 19 Oct 2012 18:30:29 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arch@...r.kernel.org" <linus-arch@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Haavard Skinnemoen <hskinnemoen@...il.com>,
	Mike Frysinger <vapier@...too.org>,
	Jesper Nilsson <jesper.nilsson@...s.com>,
	David Howells <dhowells@...hat.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Hirokazu Takata <takata@...ux-m32r.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Michal Simek <monstr@...str.eu>,
	Jonas Bonn <jonas@...thpole.se>,
	"James E.J. Bottomley" <jejb@...isc-linux.org>,
	Richard Kuo <rkuo@...eaurora.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Lennox Wu <lennox.wu@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Paul Mundt <lethal@...ux-sh.org>,
	Chris Zankel <chris@...kel.net>,
	Chris Metcalf <cmetcalf@...era.com>,
	Yoshinori Sato <ysato@...rs.sourceforge.jp>,
	Guan Xuetao <gxt@...c.pku.edu.cn>
Subject: Re: new execve/kernel_thread design

On Fri, Oct 19, 2012 at 05:16:50PM +0000, Luck, Tony wrote:
> > Surprisingly enough, ia64 one seems to work on actual hardware; I have sent
> > Tony an incremental patch cleaning copy_thread() up, waiting for results of
> > testing that on SMP box.
> 
> Tiny bit faster than plain 3.7-rc1. lmbench3 reports fork+execve test at between
> 558 to 567 usec with the new code, compared with 562-572 usec with the old.

Are you OK with the state of comments in call_payload() in the current
form of that sucker?  Right now in #arch-ia64 is looks so:
ENTRY(call_payload)
        .prologue ASM_UNW_PRLG_RP|ASM_UNW_PRLG_PFS, ASM_UNW_PRLG_GRSAVE(0)
        /* call the kernel_thread payload; fn is in r4, arg - in r5 */
        alloc loc1=ar.pfs,0,3,1,0
        mov loc0=rp
        mov loc2=gp
        mov out0=r5             // arg
        ld8 r14 = [r4], 8       // fn.address
        ;;
        mov b6 = r14
        ld8 gp = [r4]           // fn.gp
        ;;
        br.call.sptk.many rp=b6 // fn(arg)
.ret12: mov gp=loc2
        mov rp=loc0
        mov ar.pfs=loc1
        /* ... and if it has returned, we are going to userland */
        cmp.ne pKStk,pUStk=r0,r0
        br.ret.sptk.many rp
END(call_payload)

IIRC, the lack of comments on function with unusual calling conventions was
the last remaining issue...
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