1
99:59:59,999 --> 99:59:59,999
So hi there, everyone.

2
99:59:59,999 --> 99:59:59,999
My name is Chandler Carruth.

3
99:59:59,999 --> 99:59:59,999
I work for Google

4
99:59:59,999 --> 99:59:59,999
I work on our C++ language platform

5
99:59:59,999 --> 99:59:59,999
I work on our C++ compilers

6
99:59:59,999 --> 99:59:59,999
specifically the Clang and LLVM teams at Google

7
99:59:59,999 --> 99:59:59,999
And I'm here to talk to you a little about performance.

8
99:59:59,999 --> 99:59:59,999
and efficiency, and making code fast,

9
99:59:59,999 --> 99:59:59,999
and all the different things that go into that.

10
99:59:59,999 --> 99:59:59,999
But before I do too much

11
99:59:59,999 --> 99:59:59,999
I want to give actually give you guys a little bit of

12
99:59:59,999 --> 99:59:59,999
one might say are expectations.

13
99:59:59,999 --> 99:59:59,999
Because I have been reading the twitter feed

14
99:59:59,999 --> 99:59:59,999
from all these folks, that talk about

15
99:59:59,999 --> 99:59:59,999
all these crazy good questions

16
99:59:59,999 --> 99:59:59,999
I just want you guys to essentially know

17
99:59:59,999 --> 99:59:59,999
this is my view

18
99:59:59,999 --> 99:59:59,999
of what Performance 101 should be.

19
99:59:59,999 --> 99:59:59,999
Okay? This is going to be kind of an intro talk.

20
99:59:59,999 --> 99:59:59,999
You guys are hard core, really deep performance nuts.

21
99:59:59,999 --> 99:59:59,999
You may be a little bit bored, and please be kind,

22
99:59:59,999 --> 99:59:59,999
because I'm going to gloss over some things

23
99:59:59,999 --> 99:59:59,999
you could heckle me thoroughly if you really want to

24
99:59:59,999 --> 99:59:59,999
We're going to talk about efficiency, performance,

25
99:59:59,999 --> 99:59:59,999
algorithms and data structures.

26
99:59:59,999 --> 99:59:59,999
And the first thing we are going to do is we're not going to talk about them.

27
99:59:59,999 --> 99:59:59,999
We're going to talk about why anyone cares about them.

28
99:59:59,999 --> 99:59:59,999
How many folks here think it's really important

29
99:59:59,999 --> 99:59:59,999
to have high performance in C++?

30
99:59:59,999 --> 99:59:59,999
Raise your hand if think that it's super important.

31
99:59:59,999 --> 99:59:59,999
Everyone thinks it's important!

32
99:59:59,999 --> 99:59:59,999
And the folks here who have a really clear idea why performance is important.

33
99:59:59,999 --> 99:59:59,999
Now, all the people who didn't raise their hands the second time,

34
99:59:59,999 --> 99:59:59,999
Please reconsider raising your hand the first time.

35
99:59:59,999 --> 99:59:59,999
We actually need to understand why performance is important in C++,

36
99:59:59,999 --> 99:59:59,999
before we actually decide it's important, we're going to care a lot about it.

37
99:59:59,999 --> 99:59:59,999
I'm going to tell you why I care about performance in C++.

38
99:59:59,999 --> 99:59:59,999
Most of it comes down to a quote from Nicolas Werth.

39
99:59:59,999 --> 99:59:59,999
Which I will try to pronounce correctly but fail miserably.

40
99:59:59,999 --> 99:59:59,999
I actually really like a lot of our stuff,

41
99:59:59,999 --> 99:59:59,999
I think he encapsulates a lot of my thoughts,

42
99:59:59,999 --> 99:59:59,999
what's core to my philosophy here.

43
99:59:59,999 --> 99:59:59,999
The software is getting slower more rapidly than

44
99:59:59,999 --> 99:59:59,999
hardware becomes faster.

45
99:59:59,999 --> 99:59:59,999
This is particularly in contrast to

46
99:59:59,999 --> 99:59:59,999
the kind of normal Moore's Law approach:

47
99:59:59,999 --> 99:59:59,999
Hardware's getting faster, all the time

48
99:59:59,999 --> 99:59:59,999
it's okay, we don't need to make software faster,

49
99:59:59,999 --> 99:59:59,999
because the hardware will catch up.

50
99:59:59,999 --> 99:59:59,999
And it turns out that's not really true.

51
99:59:59,999 --> 99:59:59,999
We're really good at writing slow software.

52
99:59:59,999 --> 99:59:59,999
Even in C++, we're really good at writing slow software.

53
99:59:59,999 --> 99:59:59,999
It's hard to write fast software,

54
99:59:59,999 --> 99:59:59,999
and it takes a lot of effort.

55
99:59:59,999 --> 99:59:59,999
And so it's important to think about

56
99:59:59,999 --> 99:59:59,999
why that might matter no matter how fast

57
99:59:59,999 --> 99:59:59,999
the processors get.

58
99:59:59,999 --> 99:59:59,999
And to give you an idea of just how much

59
99:59:59,999 --> 99:59:59,999
I think Nicholas Werth is on the same page

60
99:59:59,999 --> 99:59:59,999
I just have to mention he actually wrote a book

61
99:59:59,999 --> 99:59:59,999
entitled Algorithms + Data Structures = Programs.

62
99:59:59,999 --> 99:59:59,999
I did not realize this as I was picking

63
99:59:59,999 --> 99:59:59,999
the title of the topic.

64
99:59:59,999 --> 99:59:59,999
Anyways, we're going to come back

65
99:59:59,999 --> 99:59:59,999
to the title of this book.

66
99:59:59,999 --> 99:59:59,999
Because he predicted some whole elements

67
99:59:59,999 --> 99:59:59,999
of this talk in this book.

68
99:59:59,999 --> 99:59:59,999
So how many folks here have read this book?

69
99:59:59,999 --> 99:59:59,999
Anyone? All right! A long time ago.

70
99:59:59,999 --> 99:59:59,999
It's a good book. It's a good book.

71
99:59:59,999 --> 99:59:59,999
Okay, so I actually think the idea that

72
99:59:59,999 --> 99:59:59,999
software is getting slower too quickly, right?

73
99:59:59,999 --> 99:59:59,999
is really getting slower at an astonishing

74
99:59:59,999 --> 99:59:59,999
rate is even more important than before.

75
99:59:59,999 --> 99:59:59,999
And for pretty specific reasons.

76
99:59:59,999 --> 99:59:59,999
There was a very seminal event that

77
99:59:59,999 --> 99:59:59,999
happened in the technology world some time ago

78
99:59:59,999 --> 99:59:59,999
that changed, in my opinion and a lot of

79
99:59:59,999 --> 99:59:59,999
other peoples' opinion, how we look at

80
99:59:59,999 --> 99:59:59,999
computing devices, the performance of

81
99:59:59,999 --> 99:59:59,999
computing devices, the challenges we face

82
99:59:59,999 --> 99:59:59,999
running software for computing devices.

83
99:59:59,999 --> 99:59:59,999
And this event was the iPhone. Okay?

84
99:59:59,999 --> 99:59:59,999
And when Steve Jobs introduced the iPhone,

85
99:59:59,999 --> 99:59:59,999
he was not doing anything particular to C++

86
99:59:59,999 --> 99:59:59,999
but he was changing how we

87
99:59:59,999 --> 99:59:59,999
think about computing.

88
99:59:59,999 --> 99:59:59,999
Mobile was now a first class compute citizen.

89
99:59:59,999 --> 99:59:59,999
It took the world a little while to even

90
99:59:59,999 --> 99:59:59,999
realize that that was what had happened that day.

91
99:59:59,999 --> 99:59:59,999
But that's what happened.

92
99:59:59,999 --> 99:59:59,999
We now have to care about mobile.

93
99:59:59,999 --> 99:59:59,999
We have to care about things that are small.

94
99:59:59,999 --> 99:59:59,999
Right? things that are hard and challenging

95
99:59:59,999 --> 99:59:59,999
to fit big bulky systems into.

96
99:59:59,999 --> 99:59:59,999
And we essentially get into this annoying

97
99:59:59,999 --> 99:59:59,999
situation of, we have small, we have fast

98
99:59:59,999 --> 99:59:59,999
machines. We have to choose one.

99
99:59:59,999 --> 99:59:59,999
We don't get to choose though.

100
99:59:59,999 --> 99:59:59,999
We're going to choose small almost every time.

101
99:59:59,999 --> 99:59:59,999
But it gets worse.

102
99:59:59,999 --> 99:59:59,999
Because the other problem that the iPhone

103
99:59:59,999 --> 99:59:59,999
introduced that people weren't

104
99:59:59,999 --> 99:59:59,999
really focused on at the time

105
99:59:59,999 --> 99:59:59,999
was the problem of a battery.

106
99:59:59,999 --> 99:59:59,999
What do we do about the battery in your phone?

107
99:59:59,999 --> 99:59:59,999
You phone's battery, I mean my phone's

108
99:59:59,999 --> 99:59:59,999
battery is about dead. Right?

109
99:59:59,999 --> 99:59:59,999
How many folks here have charged their

110
99:59:59,999 --> 99:59:59,999
phone today? (Laughter from audience) Okay?

111
99:59:59,999 --> 99:59:59,999
That's a problem. That's not a feature.

112
99:59:59,999 --> 99:59:59,999
That's a bug. (Laughter from audience) Okay?

113
99:59:59,999 --> 99:59:59,999
Yes, How many folks are charging their phone now?

114
99:59:59,999 --> 99:59:59,999
(Laughter from audience) Okay so we kind of

115
99:59:59,999 --> 99:59:59,999
entered this new problem domain, suddenly

116
99:59:59,999 --> 99:59:59,999
power became relevant.

117
99:59:59,999 --> 99:59:59,999
There's some kind of shady research I want

118
99:59:59,999 --> 99:59:59,999
to push back against.

119
99:59:59,999 --> 99:59:59,999
There's some research into power efficient

120
99:59:59,999 --> 99:59:59,999
instructions. If you ever read about power

121
99:59:59,999 --> 99:59:59,999
efficient instructions or optimizing

122
99:59:59,999 --> 99:59:59,999
power usage, you should become very suspicious.

123
99:59:59,999 --> 99:59:59,999
And you should probably run the other direction.

124
99:59:59,999 --> 99:59:59,999
Because this is mostly total junk science. Okay?

125
99:59:59,999 --> 99:59:59,999
Here's the number one leading theory

126
99:59:59,999 --> 99:59:59,999
about how to save this, how to save

127
99:59:59,999 --> 99:59:59,999
battery life. Finish running the program.

128
99:59:59,999 --> 99:59:59,999
(Audience laughter) Seriously, race to sleep.

129
99:59:59,999 --> 99:59:59,999
That's the actual technical term, race to sleep.

130
99:59:59,999 --> 99:59:59,999
The faster your software runs, the less

131
99:59:59,999 --> 99:59:59,999
power it consumes. Now people get really

132
99:59:59,999 --> 99:59:59,999
upset about this. No, no if I run

133
99:59:59,999 --> 99:59:59,999
software really fast, then it heats up my

134
99:59:59,999 --> 99:59:59,999
processor, all that excess heat, that's the

135
99:59:59,999 --> 99:59:59,999
wasted power. But it's not, okay? Here's

136
99:59:59,999 --> 99:59:59,999
the thing, we've never really figured out

137
99:59:59,999 --> 99:59:59,999
how to run processors and do work

138
99:59:59,999 --> 99:59:59,999
on processors in a

139
99:59:59,999 --> 99:59:59,999
power efficient way. Do you know what we

140
99:59:59,999 --> 99:59:59,999
have figured out how to do with processors

141
99:59:59,999 --> 99:59:59,999
that has made our battery lives improve

142
99:59:59,999 --> 99:59:59,999
over time? We figured out how to turn them off.

143
99:59:59,999 --> 99:59:59,999
This is literally how your phone, your

144
99:59:59,999 --> 99:59:59,999
laptop, like if you have your computer

145
99:59:59,999 --> 99:59:59,999
on your desk. Every single

146
99:59:59,999 --> 99:59:59,999
microprocessor, general purpose

147
99:59:59,999 --> 99:59:59,999
microprocessors you can get today.

148
99:59:59,999 --> 99:59:59,999
The way it conserves power is by

149
99:59:59,999 --> 99:59:59,999
turning itself off as rapidly and as

150
99:59:59,999 --> 99:59:59,999
frequently as possible for as long a

151
99:59:59,999 --> 99:59:59,999
period time as possible. The more

152
99:59:59,999 --> 99:59:59,999
your processor turns on, the less this

153
99:59:59,999 --> 99:59:59,999
little green goes yellow and then red.

154
99:59:59,999 --> 99:59:59,999
Bad stuff right? So we actually want to

155
99:59:59,999 --> 99:59:59,999
make code faster in order to save battery

156
99:59:59,999 --> 99:59:59,999
life. Universally, this is true.

157
99:59:59,999 --> 99:59:59,999
There are some extreme exceptions to it

158
99:59:59,999 --> 99:59:59,999
There'e some really weird stuff around

159
99:59:59,999 --> 99:59:59,999
out on the fringe. But 99.999999% of the time

160
99:59:59,999 --> 99:59:59,999
You want to run code faster to save

161
99:59:59,999 --> 99:59:59,999
battery. But batteries aren't the only

162
99:59:59,999 --> 99:59:59,999
story when it comes to saving power.

163
99:59:59,999 --> 99:59:59,999
This is one of Google's data centers.

164
99:59:59,999 --> 99:59:59,999
You'll note that this is a very large building

165
99:59:59,999 --> 99:59:59,999
and the only thing it is doing is taking

166
99:59:59,999 --> 99:59:59,999
electricity and turning it into heat.

167
99:59:59,999 --> 99:59:59,999
That is it's job. And it's really good

168
99:59:59,999 --> 99:59:59,999
at it's job. And unfortunately,

169
99:59:59,999 --> 99:59:59,999
electricity costs a lot of money.

170
99:59:59,999 --> 99:59:59,999
And in fact, it's a finite resource.

171
99:59:59,999 --> 99:59:59,999
There's a certain point at which the cost

172
99:59:59,999 --> 99:59:59,999
goes away, you simply cannot have any

173
99:59:59,999 --> 99:59:59,999
more electricity at a particular point

174
99:59:59,999 --> 99:59:59,999
in time. And so power becomes very, very

175
99:59:59,999 --> 99:59:59,999
important in a data center as well.

176
99:59:59,999 --> 99:59:59,999
And I find it interesting that it's on the

177
99:59:59,999 --> 99:59:59,999
two extremes of computing platforms that

178
99:59:59,999 --> 99:59:59,999
we find convergence. Right? When you drop

179
99:59:59,999 --> 99:59:59,999
to a phone, or you go up to a data center

180
99:59:59,999 --> 99:59:59,999
all of a sudden power dominates. Right?

181
99:59:59,999 --> 99:59:59,999
We'll talk about compute per watt.

182
99:59:59,999 --> 99:59:59,999
This is another picture of the data center

183
99:59:59,999 --> 99:59:59,999
by the way. I just want to clarify what

184
99:59:59,999 --> 99:59:59,999
this is. This is one of my favorite pictures

185
99:59:59,999 --> 99:59:59,999
Those are enormous vents blowing out stem vapor.

186
99:59:59,999 --> 99:59:59,999
I don't know much about this but

187
99:59:59,999 --> 99:59:59,999
apparently when you can see the water vapor

188
99:59:59,999 --> 99:59:59,999
the data center is operating at peak

189
99:59:59,999 --> 99:59:59,999
efficiency because it means it's not too hot,

190
99:59:59,999 --> 99:59:59,999
its not too cool, its actually efficiently

191
99:59:59,999 --> 99:59:59,999
cooling the ?. Anyway this is trivia.

192
99:59:59,999 --> 99:59:59,999
So the compute per watt tends to

193
99:59:59,999 --> 99:59:59,999
dominate in the data canter and this is

194
99:59:59,999 --> 99:59:59,999
actually kind of the same thing we're trying

195
99:59:59,999 --> 99:59:59,999
to pull off on a phone or anything else.

196
99:59:59,999 --> 99:59:59,999
We want to maximize how much compute

197
99:59:59,999 --> 99:59:59,999
we can get out of the watts we're going

198
99:59:59,999 --> 99:59:59,999
to burn when the chip is turned on.

199
99:59:59,999 --> 99:59:59,999
Makes sense? Alright? Now I say raw speed

200
99:59:59,999 --> 99:59:59,999
isn't everything because when we talk

201
99:59:59,999 --> 99:59:59,999
about performance as really important

202
99:59:59,999 --> 99:59:59,999
you'll get some mixed messages from people.

203
99:59:59,999 --> 99:59:59,999
How many folks(8:34)