front end to gcc

“speed is the one truly modern pleasure.” Aldous Huxley

previous work

• NFS
• same libraries
• synchronised clocks
• single administrator
• a lot of hassle

Requirements

• run jobs in parallel
• same output
• must be correct

Phases of compiling

• preprocess, include files
• compile preprocessed source

• link together object files

    export DISTCC_HOSTS="a b c ..."
    make CC=distcc -j6
  

is gain > overhead time?

• kernel efficient at sending bulk data
• some projects, e.g. OpenOffice assume sequential execution
• good projects, code that is hard to compile, e.g. C++

problems

• object file gcc 2.96 won’t work with gcc 3.2
• check gcc version not enough; check vendor specific patches?
• C++ ABI issues
• Makefile bugs, race conditions, etc
• kernel bugs detected, TCP round trip timer, now fixed; time doesn’t go backwards even if going too fast
• precompiled headers - especially for C++ templates
• integrated headers

scheduling

• make doesn’t expose global information, distcc doesn’t know what it needs to know
• best throughput desired

compression

• LZO fast compressor
• 1:2 to 1:3
• good when network is the limiting factor

SSH

• a bit slow, but feasible
• access, privacy, integrity all taken care of

performance hacks

• preforked daemons
• sendfile to send the file other the network
• mmap
• TTCP corks

scalability

• recursive make considered possible

KISS = Keep it simple & safe

• No central coordinator
• minarchy
• clients remember hitns about down/busy hosts
• fall back to running gcc