linux-kernel - Re: [RFC] User space to kernel space copy optimization

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Date:	Mon, 16 Nov 2015 22:57:47 +0000
From:	"Jiang, Dave" <dave.jiang@...el.com>
To:	"dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
	"okaya@...eaurora.org" <okaya@...eaurora.org>
CC:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] User space to kernel space copy optimization



On Mon, 2015-11-16 at 21:53 +0000, Sinan Kaya wrote:
> One of the things I'm interested in is to use a memcpy capable DMA
> engine HW to optimize user space and kernel space parameter copying.

Have you looked at why NET_DMA was deprecated and using DMA engine to
do kernel->user copy could be a problem?
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/
?id=77873803363c

> 
> Of course, this will not be viable for all parameter sizes but I can
> see
> this being useful. The goal is to save power in the cost of little
> performance.
> 
> Before I go and invent my own mechanism, I'd like to have ideas on
> what
> an acceptable solution would look like. Especially, I'm looking for a
> generic implementation that could plug into any DMA engine HW.
> 
> -- 
> Sinan Kaya
> Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center,
> Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
> Linux Foundation Collaborative Project
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