On 7/31/19 9:40 AM, Jan Hubicka wrote: >> Neither will work very well, we have thousands of -flto tests outside of >> lto.exp, e.g. dg-torture.exp (or libgomp and others) cycle through various >> options including -flto etc. >> >> Some env var would be useful I guess, though shouldn't it have GCC in the >> name? I mean, if we run into these fork-bomb problems in gcc, won't other >> projects run into those as well? >> >> Why doesn't the jobserver work in the tests? Is that because of missing + >> somewhere in the Makefiles or is something unsetting MFLAGS or MAKEFLAGS >> env vars? > > Main trouble with make's jobserver is that it works by > 1) defining environment variable saying which file descriptior to > connect to > 2) keeping the file descriptor open upon invoking "+" prefixed lines > > Adding "+" to GCC invocation is wrong since it breaks dry run (we do not > want to link at that time) but it is only way to access the jobserver. > If "+" is not present, make will keep the environment vairable but will > close file descriptors prior exec. > > Make developers said that this is because some old prorams misbehave > when you exec them with more than 3 file descriptors open. I tried to > negotiate for named pipe which would solve this and it would make it > easy to connect to outermost jobserver from anything invoked form > toplevel make, but they was worried about systems w/o named pipes.
Yes a more generic approach would be welcome as other build systems would also be able to utilize it. > > I wonder why we do not detect jobserv as unavailable in this case and do > not default to -flto=<numthreads>? We do not detect jobserver because of Dejagnu is not using it. And yes, we default to -flto=<numthreads> in LTO tests now. That's what is causing issues right now. > Is it because dejagnu machinery actually opens some other file > descriptor that gets same ID and executes us with it? > > Or does LTO wrapper open something prior accessing jobserver? > >> >> Though, as I said on IRC, I think we might run out of filedescriptors when >> using jobserver too, say if on 64 thread machine one does make -j64 -k check >> and each test simultaneously tries to create 64 partitions, that would be >> 4096 connections to the jobserver, right? > > Only WPA process connects to jobserver (which is 1 per linker > invokation), so I think this should be safe. Yes and it's only about a quick fcntl. But as mentioned, Dejagnu is not passing us jobserver, so we don't do it right now. Martin > > Honza >> >> Jakub
