X neotest/bench-disk: Deduplicate code; change 1M -> 2M

So now we are benchmarking disk for sizes 4K and 2M which are the usual
sizes popping up with e.g. wendelin.core.

go/neo/t/neotest

@@ -856,7 +856,6 @@ bench_cpu() {
 bench_disk() {
 	# ioping2bench <topic>	- converts timings from ioping to std benchmark
 	ioping2bench() {
-		# XXX normalize all units to µs (benchstat treats time and µs as different - XXX better improve benchstat)
 		# min/avg/max/mdev = 102.2 us / 138.6 us / 403.3 us / 12.2 us
 		sed -u -e \
 		"s|^min/avg/max/mdev = \([0-9.]\+\) \([^ ]\+\) / \([0-9.]\+\) \([^ ]\+\) / \([0-9.]\+\)\+ \([^ ]\+\) / \([0-9.]\+\) \([^ ]\+\)\$|&\n\
@@ -865,26 +864,27 @@ Benchmark$1-avg 1 \\3 \\4/op\
 |"
 	}
 
-	echo -e "\n*** disk: random direct (no kernel cache) 4K-read latency"
-	nrun ioping -D -i 0ms -s 4k -S 1024M -w 3s -q -k . |\
-		ioping2bench "`hostname`/disk/randread/direct/4K"
+	#sizev="1K 4K 1M 2M"
+	sizev="4K 2M"
+	benchtime=3s
+
+	for size in $sizev; do
+		echo -e "\n*** disk: random direct (no kernel cache) $size-read latency"
+		nrun ioping -D -i 0ms -s $size -S 1024M -w $benchtime -q -k . |\
+			ioping2bench "`hostname`/disk/randread/direct/$size"
+	done
 
-	echo -e "\n*** disk: random direct (no kernel cache) 1M-read latency"
-	nrun ioping -D -i 0ms -s 1M -S 1024M -w 3s -q -k . |\
-		ioping2bench "`hostname`/disk/randread/direct/1M"
 
-	echo -e "\n*** disk: random cached 4K-read latency"
 	# warmup so kernel puts the file into pagecache
 	for i in `seq 3`; do
 		cat ioping.tmp >/dev/null
 	done
 
-	nrun ioping -C -i 0ms -s 4k -S 1024M -w 3s -q -k . |\
-		ioping2bench "`hostname`/disk/randread/pagecache/4K"
-
-	echo -e "\n*** disk: random cached 1M-read latency"
-	nrun ioping -C -i 0ms -s 1M -S 1024M -w 3s -q -k . |\
-		ioping2bench "`hostname`/disk/randread/pagecache/1M"
+	for size in $sizev; do
+		echo -e "\n*** disk: random cached $size-read latency"
+		nrun ioping -C -i 0ms -s $size -S 1024M -w $benchtime -q -k . |\
+			ioping2bench "`hostname`/disk/randread/pagecache/$size"
+	done
 }
 
 # hash function to compute via zhash in tests/benchmarks
@@ -1023,7 +1023,6 @@ cmd_bench-cluster() {
 	# ping2bench <topic>	- converts timings from ping to std benchmark format
 	ping2bench() {
 		# rtt min/avg/max/mdev = 0.028/0.031/0.064/0.007 ms, ipg/ewma 0.038/0.032 ms
-		# XXX normalize to µs
 		sed -u -e \
 		"s|^rtt min/avg/max/mdev = \([0-9.]\+\)/\([0-9.]\+\)/\([0-9.]\+\)/\([0-9.]\+\) ms.*\$|&\n\
 Benchmark$1-min 1 \\1 ms/op\n\