Re: 【Question】Whether it's legal to enable same physical DMA memory mapped for different NIC device?

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Wed, Dec 07, 2011 at 10:16:40PM +0800, ustc.mail wrote:
> Dear all,
> 
> In NIC driver, to eliminate the  overhead of dma_map_single() for DMA
> packet data,  we have statically allocated huge DMA memory buffer ring
> at once instead of calling dma_map_single() per packet.  Considering
> to further reduce the copy overhead between different NIC(port) ring
> while forwarding, one packet from a input NIC(port) will be
> transferred to output NIC(port) with no any copy action.
> 
> To satisfy this requirement, the packet memory should be mapped into
> input port and unmapped when leaving input port, then mapped into
> output port and unmapped later.
> 
> Whether it's legal to map the same DMA memory into input and output
> port simultaneously? If it's not, then the zero-copy for packet
> forwarding is not feasible?
> 

Did you ever a get a response about this?

Is the output/input port on a seperate device function? Or is it
just a specific MMIO BAR in your PCI device?

> Hope PCI expert to post your suggestion.
> 
> Thanks!
> 
> --Yanfei
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-pci" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html