Re: [PATCH] mm: add an option to disable bounce
From: KOSAKI Motohiro
Date: Mon Apr 29 2013 - 16:46:25 EST
(4/22/13 11:23 AM), vinayakm.list@xxxxxxxxx wrote:
> From: Vinayak Menon <vinayakm.list@xxxxxxxxx>
> There are times when HIGHMEM is enabled, but
> we don't prefer CONFIG_BOUNCE to be enabled.
> CONFIG_BOUNCE can reduce the block device
> throughput, and this is not ideal for machines
> where we don't gain much by enabling it. So
> provide an option to deselect CONFIG_BOUNCE. The
> observation was made while measuring eMMC throughput
> using iozone on an ARM device with 1GB RAM.
> Signed-off-by: Vinayak Menon <vinayakm.list@xxxxxxxxx>
> mm/Kconfig | 6 ++++++
> 1 file changed, 6 insertions(+)
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 3bea74f..29f9736 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -263,8 +263,14 @@ config ZONE_DMA_FLAG
> default "1"
> config BOUNCE
> + bool "Enable bounce buffers"
> def_bool y
> depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
> + help
> + Enable bounce buffers for devices that cannot access
> + the full range of memory available to the CPU. Enabled
> + by default when ZONE_DMA or HIGMEM is selected, but you
> + may say n to override this.
This should depend on CONFIG_EXPERT. Because this makes typically worse result
on typical desktop machine.
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