linux-kernel - RE: [RFC PATCH v3 7/7] x86/unwind/orc: remove run-time ORC unwind tables sort

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Message-ID: <893d3caf85cd4ed0921fab84cfe28cad@AcuMS.aculab.com>
Date:   Fri, 15 Nov 2019 16:51:24 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Shile Zhang' <shile.zhang@...ux.alibaba.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "x86@...nel.org" <x86@...nel.org>
CC:     "H . Peter Anvin" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>
Subject: RE: [RFC PATCH v3 7/7] x86/unwind/orc: remove run-time ORC unwind
 tables sort

From: Shile Zhang
> Sent: 15 November 2019 06:48
...
>  arch/x86/kernel/unwind_orc.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
> index 332ae6530fa8..280da6fa9922 100644
> --- a/arch/x86/kernel/unwind_orc.c
> +++ b/arch/x86/kernel/unwind_orc.c
> @@ -273,9 +273,11 @@ void __init unwind_init(void)
>  		return;
>  	}
> 
> -	/* Sort the .orc_unwind and .orc_unwind_ip tables: */
> -	sort(__start_orc_unwind_ip, num_entries, sizeof(int), orc_sort_cmp,
> -	     orc_sort_swap);
> +	/*
> +	 * Note, orc_unwind and orc_unwind_ip tables has been sorted in
> +	 * vmlinux link phase by sorttable tool at build time.
> +	 * Its ready for binary search now.
> +	 */

How fast is sort() if the table is sorted?
Relying on the kernel sources and build scripts always being in sync seems dangerous.
Probably better to leave the sort in for a release of two.

	David

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