After running it I saw the event loop, that was not the issue. I checked the other threads:

ide/background.cpp

void GatherAllFiles(const String& path, Index<String>& filei, VectorMap<String, String>& file)
{
    Sleep(0); // This is supposed to be superlazy
    for(FindFile ff(path + "/*.*"); ff && !Thread::IsShutdownThreads(); ff.Next())
        if(ff.IsFolder() && *ff.GetName() != '.')
            GatherAllFiles(ff.GetPath(), filei, file);
        else
        if(ff.IsFile()) {
            String p = NormalizePath(ff.GetPath());
            String lp = ToLower(p);
            if(filei.Find(lp) < 0) {
                filei.Add(lp);
                file.Add(GetFileName(p), p);
            }
        }
}

That Sleep(0) seems to be not very superlazy at all. If I set it to 10 the CPU usage drops. Could this be that Linux handles sleep differently from Windows? I can see the unix version is using nanosleep and I'm not sure what that does with a param of 0 but I'm assuming from what I've read it does nothing... which instead of making it lazy makes it expensive.

void IdeBackgroundThread()
{
	while(!Thread::IsShutdownThreads()) {
		VectorMap<String, String> file;
		Index<String> dir;
		Index<String> filei;
		
		for(FindFile ff(ConfigFile("*.var")); ff && !Thread::IsShutdownThreads(); ff.Next()) {
			VectorMap<String, String> var;
			LoadVarFile(ff.GetPath(), var);
			for(String d : Split(var.Get("UPP", ""), ';'))
				dir.FindAdd(NormalizePath(d));
			Sleep(0);
		}
		for(String d : dir)
			GatherAllFiles(d, filei, file);
		{
			Mutex::Lock __(s_allfiles_lock);
			s_allfiles = pick(file);
			s_allnests = dir.PickKeys();
		}
		for(int i = 0; i < 10 && !Thread::IsShutdownThreads(); i++)
			Sleep(100);
	}
}