-speed: print cpu model

When somebody posts "gocryptfs -speed" results, they are
most helpful together with the CPU model. Add the cpu model
to the output.

Example:

$ ./gocryptfs -speed
gocryptfs v2.2.0-beta1-5-g52b0444-dirty; go-fuse v2.1.1-0.20210825171523-3ab5d95a30ae; 2021-09-14 go1.17.1 linux/amd64
cpu: Intel(R) Core(TM) i5-3470 CPU @ 3.20GHz; with AES acceleration
AES-GCM-256-OpenSSL       	 862.79 MB/s
AES-GCM-256-Go            	 997.71 MB/s	(selected in auto mode)
AES-SIV-512-Go            	 159.58 MB/s
XChaCha20-Poly1305-OpenSSL	 729.65 MB/s
XChaCha20-Poly1305-Go     	 843.97 MB/s	(selected in auto mode)

3 files changed, 71 insertions, 6 deletions

diff --git a/README.md b/README.md
index e4ea9a7..69a3416 100644
--- a/README.md
+++ b/README.md
@@ -168,12 +168,13 @@ Example for a CPU with AES-NI:
 
 ```
 $ ./gocryptfs -speed
-gocryptfs v2.2.0-beta1-4-gcdbc48f; go-fuse v2.1.1-0.20210825171523-3ab5d95a30ae; 2021-09-14 go1.17.1 linux/amd64
-AES-GCM-256-OpenSSL          868.09 MB/s
-AES-GCM-256-Go               997.97 MB/s  (selected in auto mode)
-AES-SIV-512-Go               160.72 MB/s
-XChaCha20-Poly1305-OpenSSL   722.14 MB/s
-XChaCha20-Poly1305-Go        841.89 MB/s  (selected in auto mode)
+gocryptfs v2.2.0-beta1-5-g52b0444-dirty; go-fuse v2.1.1-0.20210825171523-3ab5d95a30ae; 2021-09-14 go1.17.1 linux/amd64
+cpu: Intel(R) Core(TM) i5-3470 CPU @ 3.20GHz; with AES acceleration
+AES-GCM-256-OpenSSL              862.79 MB/s
+AES-GCM-256-Go                   997.71 MB/s    (selected in auto mode)
+AES-SIV-512-Go                   159.58 MB/s
+XChaCha20-Poly1305-OpenSSL   729.65 MB/s
+XChaCha20-Poly1305-Go            843.97 MB/s    (selected in auto mode)
 ```
 
 You can run `./benchmark.bash` to run gocryptfs' canonical set of
diff --git a/internal/speed/cpuinfo.go b/internal/speed/cpuinfo.go
new file mode 100644
index 0000000..09e7a89
--- /dev/null
+++ b/internal/speed/cpuinfo.go
@@ -0,0 +1,54 @@
+package speed
+
+import (
+	"io/ioutil"
+	"os"
+	"runtime"
+	"strings"
+)
+
+// cpuModelName returns the "model name" acc. to /proc/cpuinfo, or ""
+// on error.
+//
+// Examples: On my desktop PC:
+//
+//   $ grep "model name" /proc/cpuinfo
+//   model name	: Intel(R) Core(TM) i5-3470 CPU @ 3.20GHz
+//
+// --> Returns "Intel(R) Core(TM) i5-3470 CPU @ 3.20GHz".
+//
+// On a Raspberry Pi 4:
+//
+//   $ grep "model name" /proc/cpuinfo
+//   (empty)
+//   $ grep Hardware /proc/cpuinfo
+//   Hardware	: BCM2835
+//
+// --> Returns "BCM2835"
+func cpuModelName() string {
+	if runtime.GOOS != "linux" {
+		return ""
+	}
+	f, err := os.Open("/proc/cpuinfo")
+	if err != nil {
+		return ""
+	}
+	content, err := ioutil.ReadAll(f)
+	if err != nil {
+		return ""
+	}
+	lines := strings.Split(string(content), "\n")
+	// Look for "model name", then for "Hardware" (arm devices don't have "model name")
+	for _, want := range []string{"model name", "Hardware"} {
+		for _, line := range lines {
+			if strings.HasPrefix(line, want) {
+				parts := strings.SplitN(line, ":", 2)
+				if len(parts) != 2 {
+					continue
+				}
+				return strings.TrimSpace(parts[1])
+			}
+		}
+	}
+	return ""
+}
diff --git a/internal/speed/speed.go b/internal/speed/speed.go
index 231a982..0b1a51a 100644
--- a/internal/speed/speed.go
+++ b/internal/speed/speed.go
@@ -27,6 +27,16 @@ const blockSize = 4096
 
 // Run - run the speed the test and print the results.
 func Run() {
+	cpu := cpuModelName()
+	if cpu == "" {
+		cpu = "unknown"
+	}
+	aes := "; no AES acceleration"
+	if stupidgcm.CpuHasAES() {
+		aes = "; with AES acceleration"
+	}
+	fmt.Printf("cpu: %s%s\n", cpu, aes)
+
 	bTable := []struct {
 		name      string
 		f         func(*testing.B)