linux-kernel - Re: [PATCH v6] usb: gadget: storage: make FSG_NUM

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Message-ID: <op.v0ha1cbg3l0zgt@mnazarewicz-glaptop>
Date:	Fri, 19 Aug 2011 22:54:38 +0200
From:	"Michal Nazarewicz" <mina86@...a86.com>
To:	"Felipe Balbi" <balbi@...com>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, linaro-dev@...ts.linaro.org,
	"Alan Stern" <stern@...land.harvard.edu>,
	"Per Forlin" <per.forlin@...aro.org>
Cc:	"Greg Kroah-Hartman" <gregkh@...e.de>
Subject: 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@...aro.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@...aro.org>

Acked-by: Michal Nazarewicz <mina86@...a86.com>

-- 
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..o | Computer Science,  Michal "mina86" Nazarewicz    (o o)
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