Benchmarking - to impress or not impress; is not even a question

2010-07-23

I love benchmarking. Benchmarking is what I do well.

There is something shimmering about running tests on a system, trying to find out what it can do. After all, who is to say that something is fast or slow? Who defines "fast", and how bad is "slow".

And, there is a but; the word "benchmarking" is badly misused and misunderstood. The goal when performing a benchmark is not to produce impressive numbers (that is called performance tuning). A benchmark will show you metrics that an isolated system with a predefined and given set of parameters can produce. It is, of course, always satisfying to show metrics which are impressive. I mean, who keeps statistics of the losing team in the last year's series of your favorite sport?

The graph below is not impressive at all, showing write performance of ca 30Mb/sec. Well, had it been 15 - 20 years ago, many companies would have paid good money to reach these numbers, but these figures were measured just recently, on a not that impressive piece of hardware stack.

[singlepic id=1 w=600 h= float=] So, what does it show?

And this is how I produced the nubers:

1) Start collecting io data

nohup iostat -d -t -k -x 10 > iostat.out &

2) Do something to produce an io load

cp -r /export/stuff/new/Favorite_tv_series.S08E1* /export/stuff/tv_serier/temp/

From here, we are set to go. We've collected data, on a given system, and we produced a well defined and reproducible workload. But what about the data? Can just about anyone graph it so nicely and be able to read what it means? For sure not. As Kevin Closson once said in a very good talk I visited; "The solution is simple, but it is not easy".

The output of iostat data looks like this:

2010-07-22T12:28:28+0200
Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s avgrq-sz avgqu-sz   await  svctm  %util
sda               0.40     0.50    0.70    0.70     6.80     4.80    16.57     0.07   47.86   7.86   1.10
sda1              0.40     0.50    0.70    0.70     6.80     4.80    16.57     0.07   47.86   7.86   1.10
sda2              0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
sda5              0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
dm-0              0.00     0.00    1.10    1.20     6.80     4.80    10.09     0.09   39.57   4.78   1.10
dm-1              0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
sdb               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
sdb1              0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
sdc               0.00     3.60    0.00   15.90     0.00    78.00     9.81     1.99  125.22   2.45   3.90
sdc1              0.00     3.60    0.00   15.90     0.00    78.00     9.81     1.99  125.22   2.45   3.90

...

2010-07-23T10:37:49+0200
Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s avgrq-sz avgqu-sz   await  svctm  %util
sda               0.00     0.30    0.00    0.50     0.00     3.20    12.80     0.01   30.00  10.00   0.50
sda1              0.00     0.30    0.00    0.50     0.00     3.20    12.80     0.01   30.00  10.00   0.50
sda2              0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
sda5              0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
dm-0              0.00     0.00    0.00    0.80     0.00     3.20     8.00     0.01   18.75   6.25   0.50
dm-1              0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
sdb               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
sdb1              0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
sdc               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
sdc1              0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00

You have to be quite darn good to graph someting like this. Even though I consider myself to possess a black belt in scripting, or perhaps because of it, I would not get at this data right away. You first have to transform it into something your favorite graph plotting tool can handle (read gnuplot). I like semicolon separated files, and I like ISO style date formats. This is what I did:

device=sdc
cat iostat.out | 
awk -v DEVICE=$device '
$1 ~ /^2010/ {
ts=$1;
gsub("T"," ",ts);
gsub("+0200","",ts);
}

$0 !~ /^$/ &&
$1 !~ /^2010/ &&
$0 !~ /Device/ &&
$1 == DEVICE {
#--- set semicolon as output field separator
OFS=";";
#--- recalculate $0 with OFS
$1=$1;
print ts, $0
}' > a.out

This is what the data looks like right now. Notice, that I filtered the data to keep only "sdc" as well:

2010-07-22 12:34:08;sdc;0.00;0.00;0.00;0.00;0.00;0.00;0.00;0.00;0.00;0.00;0.00
2010-07-22 12:34:18;sdc;0.00;0.00;0.10;0.00;0.40;0.00;8.00;0.00;20.00;20.00;0.20
2010-07-22 12:34:28;sdc;0.00;5001.40;0.00;164.30;0.00;19068.80;232.12;40.23;218.65;4.08;67.00
2010-07-22 12:34:38;sdc;0.00;6382.60;0.20;235.20;0.80;26948.80;228.97;109.58;472.74;4.00;94.20
2010-07-22 12:34:48;sdc;0.00;7032.70;0.20;250.30;0.80;29018.80;231.69;112.57;445.85;3.99;100.00
2010-07-22 12:34:58;sdc;0.00;5140.10;0.10;184.80;0.40;21379.20;231.26;47.91;265.46;4.05;74.80
2010-07-22 12:35:08;sdc;0.00;4776.10;0.20;204.80;0.80;21086.00;205.72;58.86;297.32;3.77;77.30
2010-07-22 12:35:18;sdc;0.00;4133.80;0.10;148.50;0.40;16593.20;223.33;44.39;288.05;3.84;57.10
2010-07-22 12:35:28;sdc;0.00;4056.70;0.10;149.90;0.40;17242.40;229.90;41.07;273.85;3.96;59.40
2010-07-22 12:35:38;sdc;0.00;4093.00;0.10;155.70;0.40;17115.20;219.71;40.54;269.99;3.87;60.30
2010-07-22 12:35:48;sdc;0.00;4284.60;0.00;161.30;0.00;17783.20;220.50;41.93;258.28;3.89;62.80
2010-07-22 12:35:58;sdc;0.00;0.00;0.00;0.80;0.00;3.60;9.00;0.01;350.00;1.25;0.10
2010-07-22 12:36:08;sdc;0.00;0.00;0.00;0.00;0.00;0.00;0.00;0.00;0.00;0.00;0.00

The interesting data (you know, the column with the highest values) is in the 8th column, kB written per second. So the only thing I need to do now, is to run it through gnuplot. To simplify the script a bit, I here show you the hardcoded section. In my day to day world, I just don't have the time to rewrite gnuplot scripts every time I use them, so I have written a wrapper around the whole thing so that I can reuse it.

malu@ml-sst7-0001:/home/malu/public_html/temp/quick_display/iostat $cat quickplot.gplot
reset

set terminal png size 800,400
set xdata time
set timefmt "%Y-%m-%d %H:%M:%S"
set output "pretty_picture.png"

#---  time range must be in same format as data file
set yrange [-1000:40000]
set xlabel "Date-Time"
set ylabel "kB/s"
set title "ml-sst7-0001 - kB write - from date this and that _to_ date this and that"

set datafile separator ";"

set grid
set grid front

set key right

filename="a.out"

#--- for shading offset (below the plotted line)
a=41000/20

#--- Plot the data 6 times with different shades of gray, black and green
#--- to get the illusion of having a green line with a black frame (last two plots)
#--- and a shade (the first 4 plots)
plot ["2010-07-22 12:33:00":"2010-07-22 12:40:00"] 
filename u 1:($8 - a)  w l lc rgb "#eeeeee" lw 9 t '' ,
filename u 1:($8 - a)  w l lc rgb "#dddddd" lw 7 t '', 
filename u 1:($8 - a)  w l lc rgb "#cccccc" lw 5 t '', 
filename u 1:($8 - a)  w l lc rgb "#bbbbbb" lw 3 t '', 
filename u 1:8         w l lc rgb "#555555" lw 3 t '', 
filename u 1:8         w l lc rgb "#00ff00" lw 1 t "kB/s"

And... to make the magic, make sure a.out is in the same directory, and fire off gnuplot.

cat quickplot.gplot | gnuplot

That's it, that's how I produced the graph above.

Go ahead, define your own set of tests, find out how to collect the metrics, transform the collected data into something useful, plot it, write a presentation, make a decent load of money from it. People are eager to read benchmark papers to confirm or disprove an idea, and they are very often willing to pay you a fair fee for it as well.