Re: PATCH libatomic

[Joerg Sonnenberger <joerg%bec.de@localhost>]

On Mon, May 11, 2020 at 11:38:28AM +0200, Kamil Rytarowski wrote:
> On 11.05.2020 01:49, Joerg Sonnenberger wrote:
> > On Mon, May 11, 2020 at 01:11:32AM +0200, Kamil Rytarowski wrote:
> >> On 10.05.2020 18:38, Kamil Rytarowski wrote:
> >>>  LLDB will be patched to avoid atomics.
> >> I have checked LLDB and std::atomic<uint64_t> is used on purpose and was
> >> switched from mutexes 3 years ago.
> >>
> >> https://github.com/llvm/llvm-project/commit/f9d16476573e16856bdb3250c817b0a2c631d2b1
> >>
> >> Reverting this (or rewriting) is not viable as this change improved the
> >> performance, the code was changed meanwhile and there were added two
> >> more associated std::atomic<> variables. LLDB also requires recent C++
> >> runtime.
> > 
> > Using 64bit atomics when they are present is fine. When are not
> > available, it is a huge hidden cost. This problem was discussed on the
> > LLDB mailing lists a while ago and there are essentially four possible
> > approaches:
> > 
> > (1) If there are no 64bit atomic ops, go back to using the explicit
> > mutex. This makes the cost explicit at the very least.
> 
> We agreed that the primary solution is to fallback to mutexes. This is
> what is done by libatomic.

Who is we again this time? I certainly didn't agree to it.

Joerg