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". -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
