On Fri, Apr 19, 2019 at 03:03:04PM +0200, Peter Zijlstra wrote: > On Fri, Apr 19, 2019 at 02:02:07PM +0200, Peter Zijlstra wrote: > > On Fri, Apr 19, 2019 at 12:26:47PM +0200, Peter Zijlstra wrote: > > > I thought of a horrible horrible alternative: > > > > Hurm, that's broken as heck. Let me try again. > > So I can't make that scheme work, it all ends up wanting to have > cmpxchg(). > > Do we have a performance comparison somewhere of xadd vs cmpxchg > readers? I tried looking in the old threads, but I can't seem to locate > it. > > We need new instructions :/ Or more clever than I can muster just now.
In particular, an (unsigned) saturation arithmetic variant of XADD would be very nice to have at this point.
