CppCon 2014: Chandler Carruth "Efficiency with Algorithms, Performance with Data Structures"

So Hi there, everyone.

My name is Chandler Carruth.

I work for Google

I work on our C++ language platform

I work on our C++ compilers

specifically the Clang and ?

And I'm here to talk to you a little about performance.

and efficiency, and making code fast,

and all the different things that go into that.

But before I do too much

I want to give actually give you guys a little bit of a

one might say are expectations.

Because I have been reading the twitter feed

from all these folks, that talk about all these crazy good questions

I just want you guys to essentially know this is my view

of what Performance 101 should be.

Okay? This is going to be kind of an intro talk.

You guys are hard core, really deep performance nuts.

You may be a little bit bored, and please be kind,

because I'm going to gloss over some things

you could go into thoroughly if you really want to

We're going to talk about efficiency, performance,

algorithms and data structures.

And the first thing we are going to do is we're not going to talk about them.

We're going to talk about why anyone cares about them.

How many folks here think it's really important to have high performance in C++? Like certain that it's super important?

Everyone thinks it's important!

And the folks here have a really clear idea why performance is important.

Now, all the people who didn't raise their hands the second time,

Please reconsider raising your hand the first time.

We actually need to understand why performance is important in C++,

before we actually decide it's important, we're going to care a lot about it.

I'm going to tell you why I care about performance in C++.

Most of it comes down to a quote from Nicolas Werth.

Which I will try to pronounce correctly but fail miserably.

I actually really like a lot of our stuff,

I think he really encapsulates a lot of my thoughts about the philosophy of software here.

The software is getting slower more rapidly than (1:58)

But that's what happened

We now have to care about

And we essentially

You have to choose one

We're going to choose small

The other problem

What do we do about the battery

How many folks here have charged their phone today

That's a problem.

That's not a feature, that's a bug.

How many

We've entered

Power became relevant

Power efficient instructions

Optimizing for power usage

Because this is mostly total junk science.

Here is the number one

Finish running the program

The faster your software runs, the lest

If I run

But it's not, okay?

Here's the thing.

We've only

We figured out how to turn them off.

if you have a

the way it conserves power is by turning itself off

The more

So we actually want to make code faster

There are some extreme exceptions to it

But 99.999999% of the time

But batteries aren't the only

You'll note that

The only thing it is doing is taking electricity and turning it into heat.

That is it's job

And unfortunately, electricity costs a lot of money

And so power becomes very, very important

And I find it interesting