> > The patch series changes things in stages. > > > > First we move the break/watchpoints into an array which is more > > amenable to RCU control that the QLIST. We then control the life time > > of references to break/watchpoint data by removing long held > > references in the target code and getting information when needed from > > the core. Then we stop dynamically allocation the watch/breakpoint > > data and store it directly in the array which makes iteration across > > the list a bit more cache friendly than referenced pointers. Finally > > addition and removal of elements of the array is put under RCU > > control. This ensures there is always a safe array of data to check > > in the run-loop. > > I a little bit unsure if we really want to complicate things with RCU. > Why don't we simply protect the lists with a mutex given that there's no > contention expected? BTW, as it comes to debugging, I suppose we don't > expect great performance anyway.
Mutexes do introduce some overhead. The breakpoints list are mostly touched during translation, but watchpoints aren't so we could use tb_lock for breakpoints and a separate per-CPU mutex for watchpoints. That could indeed work. Paolo
