Re: [PATCH v6] usb: gadget: storage: make FSG_NUM_BUFFERS variable size

On Fri, 19 Aug 2011 21:21:27 +0200, Per Forlin per.forlin@linaro.org wrote:

FSG_NUM_BUFFERS is set to 2 as default. Usually 2 buffers are enough to establish a good buffering pipeline. The number may be increased in order to compensate a for bursty VFS behaviour.

Here follows a description of system that may require more than 2 buffers.

• CPU ondemand governor active
• latency cost for wake up and/or frequency change
• DMA for IO

Use case description.

• Data transfer from MMC via VFS to USB.
• DMA shuffles data from MMC and to USB.
• The CPU wakes up every now and then to pass data in and out from VFS, which cause the bursty VFS behaviour.

Signed-off-by: Per Forlin per.forlin@linaro.org

Acked-by: Michal Nazarewicz mina86@mina86.com