Re: mem-to-mem copy using dma ...

[Giuseppe C. <pep...@gm...>]

Ciao Stuart,
thanks for the clarification!
To Ha Nguyen: sorry if I posted too details about the zero-copy ;-)
At any rate, concerning the network drivers optimization you could also 
look at: TSO,UFO,GSO, I/OAT, LSA,(Linux Socket Acceleration) etc. Maybe, 
you will find useful this link: http://www.linux-foundation.org/en/Net
Cheers
Peppe

Ha Nguyen wrote:
> On Feb 1, 2008 1:21 PM, Stuart MENEFY <stu...@st...> wrote:
>   
>> Folks
>>
>> Giuseppe Cavallaro wrote:
>>     
>>>> I have to read UDP packets from sk_buff to my module in kernel space and
>>>> the udp stack uses copy_to_user() to do my task. I'm wondering if using
>>>> dma for mem-to-mem copy can improve data transfer performance instead of
>>>> using copy_to_user()???
>>>>         
>>> Often to take the best performance by using a DMA engine, e.g. in a network
>>> driver,
>>> the zero-copy mechanism is used because It essentially avoids memcpy.
>>> Abut how to implement the zero-copy mechanism you ought to start looking at
>>> the network device
>>> drivers within the kernel source tree.
>>>       
>> Note that there are generally two 'copies' involved in receiving data.
>> The first is where the data is written into the network stack's packet
>> buffer, the second is where the data is copied into the user's buffer.
>> (This is ignoring the checksum step, which ideally is merged with one of
>> the other copies).
>>
>> Giuseppe is referring to removing the first, which involves the DMA engine
>> in the NIC writing the data directly into the sk_buff. Ha Nguyen was asking
>> about the second, which is very hard to remove while still retaining the
>> standard socket API.
>>     
>
> Exactly, I already configured the MAC for zero-copy. Based on Stuart's
> input, dmaengine should do my work when it is available. I'm curious
> to see if how it improves network performance...
>
> Thanks guys for your feedbacks!
>
> /ha
>