Today

• Profiling

• Static Analysis

• Developer Surveys

Profiling

What is it?

What's it good for?

When will you use it

(other than 281?)

What are its limitations

Getting started with perf

• Install the tool

sudo apt install linux-tools-common linux-tools-`uname -r`

Getting started with perf

• Install the tool

sudo apt install linux-tools-common linux-tools-`uname -r`

• Write a simple program

int main() {
    return 0;
}

• And profile it

$ make main
cc     main.c   -o main
$ perf record ./main
$ ls
main  main.c  perf.data
$ perf report

Getting something useful from perf

• Need a program that takes some time

void child() {
    int i;
    for (i=0; i < 0xFFFFFFF; i++) { // 7 F's
        asm("nop;");
    }
}
int main() {
    int i;
    for (i=0; i < 0xFFFFFFF; i++) { // 7 F's
        asm("nop;");
    }
    child();
}

$ make main
cc     main.c   -o main
$ perf record ./main
$ perf report

Understanding a little how perf works

$ perf record -F1 ./main
$ perf report

$ perf record -F100000 ./main
$ perf report

• What does -F do?
  • (Try man perf-report, you can use / to search in man)

Can we profile library code?

• Let's write a lot of 0's

#include <string.h>
...
for (i=0; i < 0xFFFFF; i++) { // 7 F's -> 5 F's
...
char buf[0xFFFF];
...
// asm("nop");
memset(buf, 0, 0xFFFF);

Some libraries are uglier :(

• Add a printf

#include <stdio.h>
...
for (i=0; i < 0xFFFFF; i++) { // 7 F's -> 5 F's
...
// asm("nop");
printf("%d\n", i);

This can make profiling real code hard

• Don't go down blind alleys (e.g. perf annotate --stdio)

(5-10 min) Try it out

Pick any prior code you've written and try profiling it

$ perf record ./your_program
$ perf report

> The bigger the better

Are the results what you expect?

Closing thoughts on profiling

When should you profile your code?

How often should you profile your code?

Closing thoughts on profiling

When should you profile your code?

How often should you profile your code?

Other questions, thoughts about profiling?

Static Analysis

What is it?

Why is it useful?

When should you run it?

Just a little history first

Linting - the original static analysis

Just a little history first

Linting - the original static analysis

• The point: The line between style and correctness is blurry

Just a little history first

Linting - the original static analysis

• The point: The line between style and correctness is blurry

Today, the lines between compilers, linters, and static analyzers are blurring

Static Analysis in action: cppcheck

sudo apt install cppcheck

Check a single file:

mmdarden@c4cs-w17:~/share/281$ cppcheck my_compress.cpp 
Checking my_compress.cpp...
[my_compress.cpp:445]: (error) Memory leak: dict
Checking my_compress.cpp: DEBUG...
Checking my_compress.cpp: DEBUG2...

Check a whole project for everything

mmdarden@c4cs-w17:~/share/281$ cppcheck --enable=all .
...

Static Analysis in action: scan-build

sudo apt install clang

This tool dynamically re-writes make rules (!)

• Won't work if you've hardcoded g++ (should be $(CXX))

bad: bad.cpp
    g++ bad.cpp
good: good.cpp
    $(CXX) $(CPPFLAGS) $(CXXFLAGS) good.cpp

mmdarden@c4cs-w17:~/share/281$ scan-build make
...
scan-build: 7 bugs found.
scan-build: Run 'scan-view /tmp/scan-build-2016-11-30' to examine bug reports

(10 min) Try it out

Try running cppcheck and scan-build on an old project

$ cppcheck --enable=all .
$ scan-build make

Did they find any errors?

Try running them on a current project

Developer Surveys

C4CS

StackOverflow.com

Next Week

Two special topics lectures

- Wed: TBD

- Fri: TBD

Come to at least one (like usual)

- Consider coming to both if you can

- Should be fun :)

warning: end-of-semester slightly shrinks the window to turn in Advanced Exercise 13

- Double check the OH on the course calendar!