On Mon, Dec 09, 2019 at 08:56:17AM +0100, Magnus Karlsson wrote: > This patch set cleans up the ring access functions of AF_XDP in hope > that it will now be easier to understand and maintain. I used to get a > headache every time I looked at this code in order to really understand it, > but now I do think it is a lot less painful. > > The code has been simplified a lot and as a bonus we get better > performance. On my 2.0 GHz Broadwell machine with a standard default > config plus AF_XDP support and CONFIG_PREEMPT on I get the following > results in percent performance increases with this patch set compared > to without it: > > Zero-copy (-N): > rxdrop txpush l2fwd > 1 core: 4% 5% 4% > 2 cores: 1% 0% 2% > > Zero-copy with poll() (-N -p): > rxdrop txpush l2fwd > 1 core: 1% 3% 3% > 2 cores: 22% 0% 5% > > Skb mode (-S): > Shows a 0% to 1% performance improvement over the same benchmarks as > above. > > Here 1 core means that we are running the driver processing and the > application on the same core, while 2 cores means that they execute on > separate cores. The applications are from the xdpsock sample app. > > When a results says 22% better, as in the case of poll mode with 2 > cores and rxdrop, my first reaction is that it must be a > bug. Everything else shows between 0% and 5% performance > improvement. What is giving rise to 22%? A quick bisect indicates that > it is patches 2, 3, 4, 5, and 6 that are giving rise to most of this > improvement. So not one patch in particular, but something around 4% > improvement from each one of them. Note that exactly this benchmark > has previously had an extraordinary slow down compared to when running > without poll syscalls. For all the other poll tests above, the > slowdown has always been around 4% for using poll syscalls. But with > the bad performing test in question, it was above 25%. Interestingly, > after this clean up, the slow down is 4%, just like all the other poll > tests. Please take an extra peek at this so I have not messed up > something. It overall makes sense to me. Jonathan, can you also help to review?
