On 2019-12-06 02:09, Adam Light wrote:
We have several machines running Windows 10 that are quite powerful
(eg. 8 or 16 core (16 or 32 thread) processors, lots of RAM, NVMe SSD
storage). However, since upgrading to Windows 1903, we have noticed
that sometimes the compile time of our large Qt 5.12 based application
increases dramatically.
As an example, on one 16 core/32 thread machine, a debug build can
take as little as 4 minutes. However it sometimes takes 18 minutes.
This is for the exact same code, compiler, settings, etc. I can
literally do a full build that takes 4 minutes, do something, delete
the build directory and rebuild and now it takes 16 minutes. The "do
something" may be going to lunch or making a trivial change in the
code. Otherwise the state of the machine is the same (no other
heavyweight processes running, etc.)
We see this behavior both when using Qt Creator 4.10.2 to do the build
(using jom.exe) and also when done outside of Creator with calls to
qmake and then jom. All files involved in anything I mention here are
on and/or written to the local SSD. I see these issues with no
antivirus running, no backup, etc.
...
Does anyone else have any ideas of how we could change our build to
improve moc performance when Windows decides to be "slow"? Like, for
example, is there any way to have the moc calls run with only a few
moc processes running at once but have the rest of the build done with
all threads running. I'm pretty sure that the OS slowdown has
something to do with thread contention of some sort.
If anyone thinks they have run into this situation or is intimately
familiar with Windows minifilter drivers, I'm happy to share the
details behind why I think they are involved here.
Thanks for any ideas
Adam
Hi, just guessing, but it could be network related. For a quick test,
when you experience that slowdown, try pulling out the network cable
from the PC and see if the build time changes.
For a more elaborate test, consider moving your Windows build PC into
the virtual realm, say like this: Use Disk2vhd
https://docs.microsoft.com/en-us/sysinternals/downloads/disk2vhd to
migrate your C: into a .vhd file. Install Ubuntu 19.10 on the PC and
VirtualBox (or VMWare Workstation player, also free). Then load up the
.vhd file into Ubuntu and, in my case, that combo (a virtual Windows
running inside Ubuntu) builds faster than my vanilla Windows 10 ever did.
This year when 1903 arrived I saw some changes as well, the boot/startup
time is better but I felt it was slower in general than 1809. So I dug
up an old Windows 7 DVD and installed it into VMWare and reinstalled Qt
on that Windows 7. Upgrading from Windows 10 to Windows 7 made jom happy
again. So while it's impossible today to find a new PC that you can
install Windows 7 on, it is still very much possible on VirtualBox or
VMWare. Finally, since Microsoft will cease support of Windows 7 next
month, make sure *never* to browse the internet or do your email from
Windows 7, always use Ubuntu.
Rgrds Henry
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