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 <[email protected]>
Reported-by: Peter Hurley <[email protected]>
Cc: Peter Hurley <[email protected]>
Cc: Chuck Ebbert <[email protected]>
Cc: Marek Szyprowski <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: David Woodhouse <[email protected]>
Cc: Don Dutile <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Yinghai Lu <[email protected]>
Cc: [email protected]
Cc: [email protected]
---
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
--
1.9.1
On Sun, 5 Oct 2014 15:02:56 +0900
Akinobu Mita <[email protected]> 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 <[email protected]>
> Reported-by: Peter Hurley <[email protected]>
> Cc: Peter Hurley <[email protected]>
> Cc: Chuck Ebbert <[email protected]>
> Cc: Marek Szyprowski <[email protected]>
> Cc: Konrad Rzeszutek Wilk <[email protected]>
> Cc: David Woodhouse <[email protected]>
> Cc: Don Dutile <[email protected]>
> Cc: Thomas Gleixner <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: "H. Peter Anvin" <[email protected]>
> Cc: Andi Kleen <[email protected]>
> Cc: Yinghai Lu <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> ---
> 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 <[email protected]>
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 <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
---
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 <include/linux/dma-contiguous.h>.
If unsure, say "n".
2014-10-05 19:47 GMT+09:00 Chuck Ebbert <[email protected]>:
> On Sun, 5 Oct 2014 15:02:56 +0900
> Akinobu Mita <[email protected]> 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 <[email protected]>
>> Reported-by: Peter Hurley <[email protected]>
>> Cc: Peter Hurley <[email protected]>
>> Cc: Chuck Ebbert <[email protected]>
>> Cc: Marek Szyprowski <[email protected]>
>> Cc: Konrad Rzeszutek Wilk <[email protected]>
>> Cc: David Woodhouse <[email protected]>
>> Cc: Don Dutile <[email protected]>
>> Cc: Thomas Gleixner <[email protected]>
>> Cc: Ingo Molnar <[email protected]>
>> Cc: "H. Peter Anvin" <[email protected]>
>> Cc: Andi Kleen <[email protected]>
>> Cc: Yinghai Lu <[email protected]>
>> Cc: [email protected]
>> Cc: [email protected]
>> ---
>> 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.
OK, I'll add information in help text for CONFIG_CMA_SIZE_MBYTES and
CONFIG_CMA_SIZE_PERCENTAGE.
Jean's patch adds information in CONFIG_DMA_CMA, so this change doesn't
conflict his patch.
> ------------------------
>
> From: Jean Delvare <[email protected]>
> 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 <[email protected]>
> Cc: Joonsoo Kim <[email protected]>
> Cc: Greg Kroah-Hartman <[email protected]>
> ---
> 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 <include/linux/dma-contiguous.h>.
> If unsure, say "n".
>