Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751468AbaJEKsJ (ORCPT ); Sun, 5 Oct 2014 06:48:09 -0400 Received: from mail-oi0-f41.google.com ([209.85.218.41]:45099 "EHLO mail-oi0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751152AbaJEKsE (ORCPT ); Sun, 5 Oct 2014 06:48:04 -0400 Date: Sun, 5 Oct 2014 05:47:58 -0500 From: Chuck Ebbert To: Akinobu Mita Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Peter Hurley , Marek Szyprowski , Konrad Rzeszutek Wilk , David Woodhouse , Don Dutile , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andi Kleen , Yinghai Lu , x86@kernel.org, iommu@lists.linux-foundation.org, Jean Delvare Subject: Re: [PATCH] cma: make default CMA area size zero for x86 Message-ID: <20141005054758.0f9c06bd@as> In-Reply-To: <1412488976-3885-1-git-send-email-akinobu.mita@gmail.com> References: <1412488976-3885-1-git-send-email-akinobu.mita@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 5 Oct 2014 15:02:56 +0900 Akinobu Mita wrote: > This makes CMA memory area size zero for x86 in default configuration > (doesn't change on the other architectures). If default CMA size is > zero, DMA_CMA is disabled. It can be enabled by passing cma= to the > kernel. > > This makes less impact on x86. Because there is no mainline driver that > requires it for x86, and Peter Hurley reported the performance > regression, as this is trying to drive _all_ dma mapping allocations > through a _very_ small window. > > Signed-off-by: Akinobu Mita > Reported-by: Peter Hurley > Cc: Peter Hurley > Cc: Chuck Ebbert > Cc: Marek Szyprowski > Cc: Konrad Rzeszutek Wilk > Cc: David Woodhouse > Cc: Don Dutile > Cc: Thomas Gleixner > Cc: Ingo Molnar > Cc: "H. Peter Anvin" > Cc: Andi Kleen > Cc: Yinghai Lu > Cc: x86@kernel.org > Cc: iommu@lists.linux-foundation.org > --- > drivers/base/Kconfig | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig > index 4e7f0ff..92a5987e 100644 > --- a/drivers/base/Kconfig > +++ b/drivers/base/Kconfig > @@ -240,6 +240,7 @@ comment "Default contiguous memory area size:" > config CMA_SIZE_MBYTES > int "Size in Mega Bytes" > depends on !CMA_SIZE_SEL_PERCENTAGE > + default 0 if X86 > default 16 > help > Defines the size (in MiB) of the default memory area for Contiguous > @@ -248,6 +249,7 @@ config CMA_SIZE_MBYTES > config CMA_SIZE_PERCENTAGE > int "Percentage of total memory" > depends on !CMA_SIZE_SEL_MBYTES > + default 0 if X86 > default 10 > help > Defines the size of the default memory area for Contiguous Memory You probably need to add some documentation too. Jean Delvare proposed the below, before your change. If the default is going to be zero on x86, that information and some further help should be added to this. ------------------------ From: Jean Delvare Subject: [PATCH] CMA: Document cma=0 It isn't obvious that CMA can be disabled on the kernel's command line, so document it. Signed-off-by: Jean Delvare Cc: Joonsoo Kim Cc: Greg Kroah-Hartman --- Documentation/kernel-parameters.txt | 3 ++- drivers/base/Kconfig | 3 +++ 2 files changed, 5 insertions(+), 1 deletion(-) --- linux-3.17-rc7.orig/Documentation/kernel-parameters.txt 2014-09-23 13:19:06.644838292 +0200 +++ linux-3.17-rc7/Documentation/kernel-parameters.txt 2014-10-04 14:10:03.257579721 +0200 @@ -656,7 +656,8 @@ bytes respectively. Such letter suffixes Sets the size of kernel global memory area for contiguous memory allocations and optionally the placement constraint by the physical address range of - memory allocations. For more information, see + memory allocations. A value of 0 disables CMA + altogether. For more information, see include/linux/dma-contiguous.h cmo_free_hint= [PPC] Format: { yes | no } --- linux-3.17-rc7.orig/drivers/base/Kconfig 2014-09-12 16:23:14.911353676 +0200 +++ linux-3.17-rc7/drivers/base/Kconfig 2014-10-04 13:41:37.672347240 +0200 @@ -231,6 +231,9 @@ config DMA_CMA to allocate big physically-contiguous blocks of memory for use with hardware components that do not support I/O map nor scatter-gather. + You can disable CMA by specifying "cma=0" on the kernel's command + line. + For more information see . If unsure, say "n". -- 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/