Hi Suwan, On 6/21/19 11:45 AM, Suwan Kim wrote:
vhci doesn’t do dma for remote device. Actually, the real dma operation is done by network card driver. So, vhci doesn’t use and need dma address of transfer buffer of urb. When vhci supports SG, it is useful to use native SG list instead of mapped SG list because dma mapping fnuction can adjust the number of SG list that is urb->num_mapped_sgs. But hcd provides dma mapping and unmapping function by defualt.
Typo "defualt"
Moreover, it causes unnecessary dma mapping and unmapping which will be done again at the NIC driver and it wastes CPU cycles. So, implement map_urb_for_dma and unmap_urb_for_dma function for vhci in order to skip the dma mapping and unmapping procedure.
How did you verify that unnecessary dma map/unmap are happening? How many CPU cycles did you manage to reduce with this change? thanks, -- Shuah
