1) unity --replace also seems to reload compiz (will test this more)
2) disabling vertex buffer doesn't seem to do anything
3) got full trace, seems consistent across 100%cpus:

(gdb) bt
#0  0xb7782424 in __kernel_vsyscall ()
#1  0xb70ddd4b in pthread_cond_wait@@GLIBC_2.3.2 ()
    at ../nptl/sysdeps/unix/sysv/linux/i386/i686/../i486/pthread_cond_wait.S:187
#2  0xb74fd8ec in __pthread_cond_wait (cond=0x85b1680, mutex=0x85b1668)
    at forward.c:149
#3  0xb4ce86fc in ?? () from /usr/lib/i386-linux-gnu/dri/swrast_dri.so
#4  0xb4cff384 in ?? () from /usr/lib/i386-linux-gnu/dri/swrast_dri.so
#5  0xb4cffb12 in ?? () from /usr/lib/i386-linux-gnu/dri/swrast_dri.so
#6  0xb4ce5f90 in ?? () from /usr/lib/i386-linux-gnu/dri/swrast_dri.so
#7  0xb4ce55ad in ?? () from /usr/lib/i386-linux-gnu/dri/swrast_dri.so
#8  0xb4bca3dc in ?? () from /usr/lib/i386-linux-gnu/dri/swrast_dri.so
#9  0xb4bca442 in ?? () from /usr/lib/i386-linux-gnu/dri/swrast_dri.so
#10 0xb4ac8625 in ?? () from /usr/lib/i386-linux-gnu/dri/swrast_dri.so
#11 0xb4ac91c8 in ?? () from /usr/lib/i386-linux-gnu/dri/swrast_dri.so
#12 0xb4f91cd5 in ?? () from /usr/lib/i386-linux-gnu/mesa/libGL.so.1
#13 0xb4f6cdf2 in glXSwapBuffers ()
   from /usr/lib/i386-linux-gnu/mesa/libGL.so.1
#14 0xb4fd1105 in GLXDoubleBuffer::swap() const ()
   from /usr/lib/compiz/libopengl.so
#15 0xb4ff03e0 in compiz::opengl::DoubleBuffer::render(CompRegion const&, bool)
    () from /usr/lib/compiz/libopengl.so
#16 0xb4fd1669 in PrivateGLScreen::paintOutputs(std::list<CompOutput*, std::allo---Type <return> to continue, or q <return> to quit---
cator<CompOutput*> >&, unsigned int, CompRegion const&) ()
   from /usr/lib/compiz/libopengl.so
#17 0xb59533a5 in CompositeScreen::paint(std::list<CompOutput*, std::allocator<CompOutput*> >&, unsigned int) () from /usr/lib/compiz/libcomposite.so
#18 0xb5956bb0 in CompositeScreen::handlePaintTimeout() ()
   from /usr/lib/compiz/libcomposite.so
#19 0xb5956ed1 in boost::detail::function::function_obj_invoker0<boost::_bi::bind_t<bool, boost::_mfi::mf0<bool, CompositeScreen>, boost::_bi::list1<boost::_bi::value<CompositeScreen*> > >, bool>::invoke(boost::detail::function::function_buffer&) () from /usr/lib/compiz/libcomposite.so
#20 0xb7739b9a in CompTimer::triggerCallback() ()
   from /usr/lib/libcompiz_core.so.ABI-20140123
#21 0xb7739c59 in CompTimeoutSource::callback() ()
   from /usr/lib/libcompiz_core.so.ABI-20140123
#22 0xb7739d72 in sigc::internal::slot_call0<sigc::bound_mem_functor0<bool, CompTimeoutSource>, bool>::call_it(sigc::internal::slot_rep*) ()
   from /usr/lib/libcompiz_core.so.ABI-20140123
#23 0xb7738fff in CompTimeoutSource::dispatch(sigc::slot_base*) ()
   from /usr/lib/libcompiz_core.so.ABI-20140123
#24 0xb724ff41 in Glib::Source::dispatch_vfunc(_GSource*, int (*)(void*), void*) () from /usr/lib/i386-linux-gnu/libglibmm-2.4.so.1
#25 0xb71400a7 in g_main_context_dispatch ()
   from /lib/i386-linux-gnu/libglib-2.0.so.0 
#26 0xb7140468 in ?? () from /lib/i386-linux-gnu/libglib-2.0.so.0
#27 0xb714076b in g_main_loop_run () from /lib/i386-linux-gnu/libglib-2.0.so.0
#28 0xb72513a3 in Glib::MainLoop::run() ()
   from /usr/lib/i386-linux-gnu/libglibmm-2.4.so.1
#29 0xb76f0838 in compiz::private_screen::EventManager::startEventLoop(_XDisplay*) () from /usr/lib/libcompiz_core.so.ABI-20140123
#30 0xb76f089e in CompScreenImpl::eventLoop() ()
   from /usr/lib/libcompiz_core.so.ABI-20140123
#31 0x08049b52 in CompManager::run() ()
#32 0x0804930c in main ()