linux-kernel - Re: [PATCH] mm: add an option to disable bounce

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Date:	Mon, 22 Apr 2013 23:07:48 +0530
From:	vinayak <vinayakm.list@...il.com>
To:	Randy Dunlap <rdunlap@...radead.org>
CC:	linux-mm@...ck.org, akpm@...ux-foundation.org, rientjes@...gle.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: add an option to disable bounce

On Monday 22 April 2013 10:28 PM, Randy Dunlap wrote:

> On 04/22/13 08:23, vinayakm.list@...il.com wrote:
>> From: Vinayak Menon <vinayakm.list@...il.com>
>>
>> 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@...il.com>
>> ---
>>  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
> 
> 	                              HIGHMEM


Thanks. I will correct this.

> 
>> +	  may say n to override this.
>>  
>>  # On the 'tile' arch, USB OHCI needs the bounce pool since tilegx will often
>>  # have more than 4GB of memory, but we don't currently use the IOTLB to present
>>
> 
> 


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