linux-kernel - Re: [PATCH v2 00/10] uaccess: better might_sleep/might

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Date:	Wed, 22 May 2013 12:19:16 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	linux-kernel@...r.kernel.org,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	David Howells <dhowells@...hat.com>,
	Hirokazu Takata <takata@...ux-m32r.org>,
	Michal Simek <monstr@...str.eu>,
	Koichi Yasutake <yasutake.koichi@...panasonic.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Chris Metcalf <cmetcalf@...era.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-arm-kernel@...ts.infradead.org, linux-m32r@...linux-m32r.org,
	linux-m32r-ja@...linux-m32r.org, microblaze-uclinux@...e.uq.edu.au,
	linux-am33-list@...hat.com, linuxppc-dev@...ts.ozlabs.org,
	linux-arch@...r.kernel.org, linux-mm@...ck.org, kvm@...r.kernel.org
Subject: Re: [PATCH v2 00/10] uaccess: better might_sleep/might_fault behavior

On Wed, May 22, 2013 at 11:25:36AM +0200, Arnd Bergmann wrote:
> Calling might_fault() for every __get_user/__put_user is rather expensive
> because it turns what should be a single instruction (plus fixup) into an
> external function call.

We could hide it all behind CONFIG_DEBUG_ATOMIC_SLEEP just like
might_sleep() is. I'm not sure there's a point to might_fault() when
might_sleep() is a NOP.
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