documentclass{article}

usepackage{tikz}
usetikzlibrary{calc,shapes, positioning,intersections}

begin{document}
begin{tikzpicture}[node distance=-pgflinewidth]

coordinate (origin) at (0,0);
coordinate (xEnd) at (0,4);
coordinate (yEnd) at (10.5,0);

tikzset{
  mybox/.style = {
     minimum height=#1,
     minimum width=1.5cm,
     inner sep=3pt,
     rotate=90,
     draw},
  mybox/.default=10.5cm,
}

draw[->,thick, name path=xaxis] (origin) -- node [above,rotate=90] {Processors} (xEnd);
draw[->,thick, name path=yaxis] (origin) -- node [below] {Time} (yEnd);

node (src) at (0.5,3) [mybox=0.4cm] {large $src$};
node (r0) [mybox=0.7cm,below=of src] {large $radix_0$};
node (r1) [mybox=0.7cm,below=of r0] {large $radix_1$};
node (r2) [mybox=0.7cm,below=of r1] {large $radix_2$};
node (r3) [mybox=0.7cm,below=of r2] {large $radix_3$};
node (r4) [mybox=0.7cm,below=of r3] {large $radix_4$};
node (r5) [mybox=0.7cm,below=of r4] {large $radix_5$};

node (r6)  [mybox=0.7cm,below=of r5,xshift=-2cm] {large $radix_6$};
node (r7)  [mybox=0.7cm,below=of r6] {large $radix_7$};
node (r8)  [mybox=0.7cm,below=of r7] {large $radix_8$};
node (r9)  [mybox=0.7cm,below=of r8] {large $radix_9$};
node (r10)  [mybox=0.7cm,below=of r9] {large $radix_{10}$};
node (op)  [mybox=0.4cm,below=of r10] {large $output$};

node (Bsrc) [mybox=0.4cm,below =of r5,fill=gray!50] {large $src$};
node (Br0) [mybox=0.7cm,below=of Bsrc,fill=gray!50] {large $radix_0$};
node (Br1) [mybox=0.7cm,below=of Br0,fill=gray!50] {large $radix_1$};
node (Br2) [mybox=0.7cm,below=of Br1,fill=gray!50] {large $radix_2$};
node (Br3) [mybox=0.7cm,below=of Br2,fill=gray!50] {large $radix_3$};
node (Br4) [mybox=0.7cm,below=of Br3,fill=gray!50] {large $radix_4$};
node (Br5) [mybox=0.7cm,below=of Br4,fill=gray!50] {large $radix_5$};

node (r6)  at (0.65,1) [mybox=0.7cm,fill=gray!80] {large $radix_6$};
node (r7)  [mybox=0.7cm,below=of r6,fill=gray!80] {large $radix_7$};
node (r8)  [mybox=0.7cm,below=of r7,fill=gray!80] {large $radix_8$};
node (r9)  [mybox=0.7cm,below=of r8,fill=gray!80] {large $radix_9$};
node (r10)  [mybox=0.7cm,below=of r9,fill=gray!80] {large $radix_{10}$};
node (op)  [mybox=0.4cm,below=of r10,fill=gray!80] {large $output$};

end{tikzpicture}
end{document}