Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932207Ab2JRKNq (ORCPT ); Thu, 18 Oct 2012 06:13:46 -0400 Received: from mail-ie0-f174.google.com ([209.85.223.174]:38167 "EHLO mail-ie0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932091Ab2JRKNo (ORCPT ); Thu, 18 Oct 2012 06:13:44 -0400 MIME-Version: 1.0 Reply-To: mtk.manpages@gmail.com In-Reply-To: <20121018094715.GC5685@mwanda> References: <1350230064.4069.1.camel@lorien2> <20121018094715.GC5685@mwanda> From: "Michael Kerrisk (man-pages)" Date: Thu, 18 Oct 2012 12:13:23 +0200 Message-ID: Subject: Re: [PATCH] Documentation DMA-API-HOWTO.txt Add dma mapping error check usage examples To: Dan Carpenter Cc: Shuah Khan , Andrew Morton , konrad.wilk@oracle.com, rob@landley.net, joerg.roedel@amd.com, shuahkhan@gmail.com, devel@linuxdriverproject.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1394 Lines: 38 On Thu, Oct 18, 2012 at 11:47 AM, Dan Carpenter wrote: > On Sun, Oct 14, 2012 at 09:54:24AM -0600, Shuah Khan wrote: >> diff --git a/Documentation/DMA-API-HOWTO.txt b/Documentation/DMA-API-HOWTO.txt >> index a0b6250..cf1adb4 100644 >> --- a/Documentation/DMA-API-HOWTO.txt >> +++ b/Documentation/DMA-API-HOWTO.txt >> @@ -468,11 +468,46 @@ To map a single region, you do: >> size_t size = buffer->len; >> >> dma_handle = dma_map_single(dev, addr, size, direction); >> + if (unlikely(dma_mapping_error(dma_handle))) { > > Don't encourage people to put unlikely() and likely() into their > driver code. It should only be used after benchmarking both with > and without. I can't imagine how it would make a measurable > difference here. (Hi Dan) Quite. See http://blog.man7.org/2012/10/how-much-do-builtinexpect-likely-and.html I wonder how many blind uses of likely() and unlikely() in the kernel are actually degrading performance. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Author of "The Linux Programming Interface"; http://man7.org/tlpi/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/