Dot

If nothing else, remember that subgraphs must start with "cluster", yes in their identifier name, to be visually distinguishable i.e. apply label/color augh.

SVG

• graphviz tools generate svg via -Tsvg
• notugly is some XSL to beautify dot's SVG output

Examples

Generated using Graphviz 2.20.2 and postprocessing via xsltproc and notugly. I hand-wrote the dot sources.

Packed Record

A packed record-type node (click to enlarge)

digraph G {
	subgraph clusterOpteron {
		label="Quad-Core Opteron"
		node [shape=record];
		struct3 [label="{ {C0|C1|C2|C3}|{L1/L2|L1/L2|L1/L2|L1/L2}|SRI\
                (SysReq Interface)|<xbar>XBAR (Crossbar Switch)|{MCH|ncHT-HB|HT0|HT1}}"]; 
	}
} 

Rectilinear arrangement A

A rectilinear graph (click to enlarge)

digraph G {
	subgraph clusterOpteronNUMA {
		label = "2x 'Deneb' Phenom II X4 910 (45nm, AM3). 8 threads."
		Deneb0->Deneb1 [dir="both" label="2GHz 16-bit bidir\n8GB/s HyperTransport 3.0" color="blue"]
		DDR0 -> Deneb0 [dir="both" color="lightblue"]
		DDR1 -> Deneb1 [dir="both" color="lightblue"]
		HostBus -> Deneb0 [dir="both" color="darkgreen"]
		HostBus -> Deneb1 [dir="both" color="darkgreen"]
		{ rank=same; Deneb0 Deneb1 }
		{ rank=same; DDR0 DDR1 }
		Deneb0 [style=filled fillcolor=steelblue shape=box]
		Deneb1 [style=filled fillcolor=steelblue shape=box]
		DDR0 [style=filled fillcolor=grey shape=invhouse]
		DDR1 [style=filled fillcolor=grey shape=invhouse]
		HostBus [style=filled fillcolor=green shape=Msquare]
	}
}

Rectilinear arrangement B

A rectilinear graph (click to enlarge)

digraph G {
	nodesep="1"
	subgraph clusterNehalemSMP {
		DDR0 -> Nehalem0 [dir="both" color="lightblue"]
		DDR0 -> Nehalem1 [dir="both" color="lightblue"]
		Nehalem0->Nehalem1 [dir="both" label="25.6GB/s QuickPath" color="blue"]
		subgraph clusterNehalemSMP0 {
			label="DRAM may or may not be shared.";
			style=filled;
			color=lightgrey;
			{ rank=same; DDR0 }
			{ rank=same; Nehalem0 Nehalem1 }
		}
		Nehalem2->Nehalem3 [dir="both" label="25.6GB/s QuickPath" color="blue"]
		Nehalem2 -> DDR1 [dir="both" color="lightblue"]
		Nehalem3 -> DDR1 [dir="both" color="lightblue"]
		subgraph clusterNehalemSMP1 {
			labelloc="b";
			label="Each package gets its own MCH and L3 cache,\neach core its own (split) L1 and (unified) L2.";
			style=filled;
			color=lightgrey;
			{ rank=same; Nehalem2 Nehalem3 }
			{ rank=same; DDR1 }
		}
		label = "4x 'Nehalem-EP' E5520 HT Core i7 (45nm LGA1336). 32 threads."
		Nehalem1->Nehalem2 [dir="both" color="blue"]
		Nehalem3->Nehalem0 [dir="both" color="blue"]
		Nehalem0->HostBus [dir="both" color="darkgreen"]
		Nehalem1->HostBus [dir="both" color="darkgreen"]
		HostBus->Nehalem2 [dir="both" color="darkgreen"]
		HostBus->Nehalem3 [dir="both" color="darkgreen"]
		Nehalem0 [style=filled fillcolor=steelblue shape=box label="4x 2-way cores"]
		Nehalem1 [style=filled fillcolor=steelblue shape=box label="4x 2-way cores"]
		Nehalem2 [style=filled fillcolor=steelblue shape=box label="4x 2-way cores"]
		Nehalem3 [style=filled fillcolor=steelblue shape=box label="4x 2-way cores"]
		DDR0 [style=filled fillcolor=grey shape=invtrapezium]
		DDR1 [style=filled fillcolor=grey shape=trapezium]
		HostBus [style=filled fillcolor=green shape=Msquare]
	}
} 

Large flow

A large flow (click to enlarge)

digraph G {
	nodesep="0.5"
	subgraph clusterPrime {
		labelloc="b";
		compound="true"
		subgraph clusterKernel {
			label="Kernelspace (Linux epoll, FreeBSD kqueue, etc...)"
			style=filled;
			color=cadetblue;
			wqueue0 [style=filled fillcolor=steelblue shape=Mdiamond]
			wqueueN [style=filled fillcolor=steelblue shape=Mdiamond]
			wqueue0 -> nics [dir=both]
			nics [style="filled,diagonals" fillcolor=greenyellow label="Devices/IPC"]
			nics -> wqueueN [dir=both]
			{ rank=same; wqueue0 wqueueN nics }
		}
		subgraph clusterUser {
			label="Userspace (libtorque-enabled process)";
			style=filled;
			color=gold;
			evqueueN [style="diagonals,filled" fillcolor=mediumpurple shape=invtrapezium group="evq"]
			evqueue0 [style="diagonals,filled" fillcolor=mediumpurple shape=invtrapezium group="evq"]
			wqueue0 -> evqueue0 [dir=both style=bold color="blue:purple"]
			wqueueN -> evqueueN [dir=both style=bold color="blue:purple"]
			evqueue0 -> evqueueN [label="About sqrt(cpus) evqueues, usually" dir=both style=dotted color=maroon]
			API -> evqueue0 [style=bold color=purple]
			API -> evqueueN [style=bold color=purple]
			API [style=filled fillcolor=green shape=box group="evq"];
			{ rank=same; evqueue0 evqueueN }
			node [shape=record];
				thr0 [label="<t0>T0|<t1>T1|<t2>T2|<tN>TN"];
				thrN [label="<t0>T0|<t1>T1|<t2>T2|<tN>TN"];
				color=red;
			evqueue0 -> thr0:t0 [color=blue]
			evqueue0 -> thr0:t1 [color=blue]
			evqueue0 -> thr0:t2 [color=blue]
			evqueue0 -> thr0:tN [color=blue]
			evqueueN -> thrN:t0 [color=blue]
			evqueueN -> thrN:t1 [color=blue]
			evqueueN -> thrN:t2 [color=blue]
			evqueueN -> thrN:tN [color=blue]
			{ rank=same; thr0 thrN }
			thr0 -> sigtable [color=lightblue style=bold]
			thr0 -> fdtable [color=lightblue style=bold]
			thr0 -> twheel [color=lightblue style=bold]
			thrN -> sigtable [color=lightblue style=bold]
			thrN -> fdtable [color=lightblue style=bold]
			thrN -> twheel [color=lightblue style=bold]
			fdtable [style=filled fillcolor=lightgreen shape=box label="fd monads\n(array)"]
			twheel [style=filled fillcolor=lightgreen shape=box label="timer monads\n(hwheel or array)"]
			sigtable [style=filled fillcolor=lightgreen shape=box label="sig monads\n(array)"]
			sigtable -> fdtable [color=lightblue label="AIO"]
			fdtable -> buf [color=lightblue]
			fdtable -> dnsssl [color=lightblue]
			twheel -> dnsssl [color=lightblue]
			buf -> API
			{ rank=same; sigtable fdtable twheel }
			dnsssl -> API
			dnsssl [style=filled fillcolor=lightgreen shape=box label="DNS, SSL/TLS\n(adns, OpenSSL)"]
			buf [style=filled fillcolor=lightgreen shape=box label="Buffering\n(arch-adaptive)"]
			node [shape=record];
				appthr [label="<tmain>Main\nthread|<t1>T1|<t2>T2|<tN>TN"];
			cbs [style=filled fillcolor=orange shape=box label="Registered callbacks"];
			cbs -> appthr [dir=both color=darkgreen]
			sigtable -> cbs [color=green]
			fdtable -> cbs [color=green]
			twheel -> cbs [color=green]
			buf -> cbs [color=green]
			dnsssl -> cbs [color=green]
			cbs -> API;
			appthr -> API;
			/*API -> fdtable [color=blueviolet]
			API -> sigtable [color=blueviolet]
			API -> twheel [color=blueviolet]*/
		}
	}
} 

PNG

Generated with dot -Tpng, no postprocessing.

Multiple records

Multiple records (click to enlarge)

digraph G {
	nodesep="0.1"
	rankdir=RL;
	subgraph clusterPrime {
		label="SHA-1 input layout\ (b\ hashes\ per\ thread)\nNx1x1 block geometry,\ Gx1x1\ grid\ geometry";
		labelloc="b";
		compound="true"
		subgraph clusterKernel {
			color=darkgoldenrod;
			style=filled;
			label="bl0";
			b0 [style=filled,width=5,shape=record,label="{ {Hash\ set\ 1\n(512n\ bits)}\
                         |{T0[0x0]|T0[0x1]|T0[...]|T0[0xf]}|{T1[0x0]|T1[0x1]|T1[...]|T1[0xf]}|{...|...|...|...}|{Tn[0x0]|Tn[0x1]|Tn[...]|Tn[0xf]}}"];
			b1 [style=filled,width=5,shape=record,label="{ {Hash\ set\ b\n(512n\ bits)}\
                         |{T0[0x0]|T0[0x1]|T0[...]|T0[0xf]}|{T1[0x0]|T1[0x1]|T1[...]|T1[0xf]}|{...|...|...|...}|{Tn[0x0]|Tn[0x1]|Tn[...]|Tn[0xf]}}"];
			label="Input to block 1 (512*n*b bits)";
		}
		subgraph clusterUser {
			color=darkkhaki;
			style=filled;
			label="bl0";
			b2 [style=filled,width=5,shape=record,label="{ {Hash\ set\ 1\n(512n\ bits)}\
                         |{T0[0x0]|T0[0x1]|T0[...]|T0[0xf]}|{T1[0x0]|T1[0x1]|T1[...]|T1[0xf]}|{...|...|...|...}|{Tn[0x0]|Tn[0x1]|Tn[...]|Tn[0xf]}}"];
			b3 [style=filled,width=5,shape=record,label="{ {Hash\ set\ b\n(512n\ bits)}\
                         |{T0[0x0]|T0[0x1]|T0[...]|T0[0xf]}|{T1[0x0]|T1[0x1]|T1[...]|T1[0xf]}|{...|...|...|...}|{Tn[0x0]|Tn[0x1]|Tn[...]|Tn[0xf]}}"];
			label="Input to block G (512*n*b bits)";
		}
	}
}