I talked to gps today and told him I would let him know my numbers on my
machine. I will share them with everybody:
My Win32 debug clobber build (mach build after mach clobber) was 39:54.84
today, up from ~33:00 a few months ago. Not sure if it is my system.
Immediate rebuild (no-op) was 10:13.05. A second no-op rebuild was
10:32.36. It looks like every shared library and every executable got
relinked.
This is on Windows7 64-bit, with 32GB of memory, an Intel 520 SSD, and an
Intel i7-3920XM @ 2.90Ghz/3.10Ghs. (Lenovo W530, plugged in, on Maximum
Performance power setting). I was doing other things (browsing, coding) in
the foreground while these builds ran in the background.
Cheers,
Brian
On Fri, Aug 2, 2013 at 2:13 PM, Gregory Szorc g...@mozilla.com wrote:
(Cross posting. Please reply to dev.builds.)
I've noticed an increase in the number of complaints about the build
system recently. I'm not surprised. Building mozilla-central has gotten
noticeably slower. More on that below. But first, a request.
Many of the complaints I've heard have been from overhearing hallway
conversations, noticing non-directed complaints on IRC, having 3rd parties
report anecdotes, etc. *Please, please, please voice your complaints
directly at me and the build peers.* Indirectly complaining isn't a very
effective way to get attention or to spur action. I recommend posting to
dev.builds so complaints and responses are public and easily archived. If
you want a more personal conversation, just get in contact with me and I'll
be happy to explain things.
Anyway, on to the concerns.
Builds are getting slower.
http://brasstacks.mozilla.com/**gofaster/#/http://brasstacks.mozilla.com/gofaster/#/has
high-level trends for our automation infrastructure. I've also noticed
my personal machines taking ~2x longer than they did 2 years ago.
Unfortunately, I can't give you a precise breakdown over where the
increases have been because we don't do a very good job of recording these
things. This is one reason why we have better monitoring on our Q3 goals
list.
Now, on to the reasons why builds are getting slower.
# We're adding new code at a significant rate.
Here is a breakdown of source file types in the tree by Gecko version.
These are file types that are directly compiled or go through code
generation to create a compiled file.
Gecko 7: 3359 C++, 1952 C, 544 CC, 1258 XPIDL, 110 MM, 195 IPDL
Gecko 14: 3980 C++, 2345 C, 575 CC, 1268 XPIDL, 272 MM, 197 IPDL, 30 WebIDL
Gecko 21: 4606 C++, 2831 C, 1392 CC, 1295 XPIDL, 292 MM, 228 IPDL, 231
WebIDL
Gecko 25: 5211 C++, 3029 C, 1427 CC, 1268 XPIDL, 262 MM, 234 IPDL, 441
WebIDL
That nets totals of:
7: 7418
14: 8667
21: 10875
25: 11872
As you can see, we're steadily adding new source code files to the tree.
mozilla-central today has 60% more source files than Gecko 7! If you assume
number of source files is a rough approximation for compile time, it's
obvious why builds are getting slower: we're building more.
As large new browser features like WebRTC and the ECMAScript
Internationalization API continue to dump hundreds of new source files in
the tree, build times will increase. There's nothing we can do about this
short of freezing browser features. That's not going to happen.
# Header dependency hell
We have hundreds of header files that are included in hundreds or even
thousands of other C++ files. Any time one of these widely-used headers
changes, the object files get invalidated by the build system dependencies
and we have to re-invoke the compiler. This also likely invalidates ccache,
so it's just like a clobber build.
No matter what we do to the build backend to make clobber builds faster,
header dependency hell will continue to undermine this progress for
dependency builds.
I don't believe the build config group is in a position to tackle header
dependency hell at this time. We are receptive to good ideas and will work
with people to land patches. Perhaps an ad-hoc group of Platform developers
can band together to address this?
# Increased reliance on C++ language features
I *suspect* that our increased reliance on C++ language features such as
templates and new C++11 features is contributing to slower build times.
It's been long known that templates and other advanced language features
can blow up the compiler if used in certain ways. I also suspect that
modern C++11 features haven't been optimized to the extent years-old C++
features have been. Combine this with the fact compilers are working harder
than ever to optimize code and it wouldn't surprise me if a CPU cycle
invested in the compiler isn't giving the returns it used to.
I would absolutely love for a compiler wizard to sit down and profile
Gecko C++ in Clang, GCC, and MSVC. If there are things we can do to our
source or to the compilers themselves to make things faster, that could be
a huge win.
Like dependency hell, I don't believe the
