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

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Date:	Mon, 16 Nov 2015 18:19:14 -0500
From:	Sinan Kaya <okaya@...eaurora.org>
To:	"Jiang, Dave" <dave.jiang@...el.com>,
	"dmaengine@...r.kernel.org" <dmaengine@...r.kernel.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 11/16/2015 5:57 PM, Jiang, Dave 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
> 

As far as I know, the problem was the TCP/IP stack trying to work on a
buffer that was given to the DMA engine for moving. It was causing stale
data problems.

The goal was to let DMA engine move the data while TCP/IP stack was
working on something else. Then, synchronize on a known point. Of
course, when above violation happens; things break.

Are you expecting a similar problem on user space to kernel space
interaction? I think the ownership buffers are pretty much defined,
isn't it?


-- 
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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