linux-kernel - Re: [PATCH 2/5] do_div(): generic optimization for constant divisor on 32-bit machines

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Message-ID: <21544300.LSjO3j3Xy7@wuerfel>
Date:	Tue, 03 Nov 2015 10:15:13 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	kbuild test robot <lkp@...el.com>
Cc:	Nicolas Pitre <nicolas.pitre@...aro.org>, kbuild-all@...org,
	Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
	Måns Rullgård <mans@...sr.com>,
	rmk+kernel@....linux.org.uk, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] do_div(): generic optimization for constant divisor on 32-bit machines

On Tuesday 03 November 2015 13:32:17 kbuild test robot wrote:
> 
>    net/can/bcm.c: In function 'bcm_proc_show':
> >> net/can/bcm.c:223:1: warning: the frame size of 1156 bytes is larger than 1024 bytes [-Wframe-larger-than=]
>     }

Interesting, that is a lot of stack for a function that only has a couple
of local variables:

#define IFNAMSIZ        16
        char ifname[IFNAMSIZ];
        struct sock *sk = (struct sock *)m->private;
        struct bcm_sock *bo = bcm_sk(sk);
        struct bcm_op *op;


This is a parisc-allyesconfig kernel, so I assume that CONFIG_PROFILE_ALL_BRANCHES
is on, which instruments every 'if' in the kernel. If that causes problems,
we could decide to disable the do_div optimization whenever CONFIG_PROFILE_ALL_BRANCHES
is enabled.

	Arnd
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