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[RFC] User space to kernel space copy optimization

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  [RFC] User space to kernel space copy optimization Sinan Kaya <okaya@codeaurora.org> - 2015-11-16 23:00 +0100
    Re: [RFC] User space to kernel space copy optimization "Jiang, Dave" <dave.jiang@intel.com> - 2015-11-17 00:00 +0100
      Re: [RFC] User space to kernel space copy optimization Sinan Kaya <okaya@codeaurora.org> - 2015-11-17 00:20 +0100
        Re: [RFC] User space to kernel space copy optimization "Jiang, Dave" <dave.jiang@intel.com> - 2015-11-17 20:30 +0100

#1270631 — [RFC] User space to kernel space copy optimization

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.

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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#1270672

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#1270687

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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#1271595

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