Hello,
This forum focuses on issues related to Xillybus' IP core. It seems like your question is more about Vivado's timing report. I therefore suggest turning to Xilinx' forums in that matter.
Regardless, and since you're apparently into hardware acceleration, I suggest looking at section 6.6 of the host application programming guide:
http://xillybus.com/downloads/doc/xilly ... _linux.pdfRegards,
Eli