On Mon, Jun 19, 2017 at 07:59:08AM -0700, Andi Kleen wrote: > > > For comparison, can you give --per-thread a go prior to these patches > > > being applied? > > > > FWIW, I had a go with (an old) perf record on an arm64 system using > > --per-thread, and I see that no samples are recorded, which seems like a > > bug. > > > > With --per-thread, the slwodown was ~20%, whereas with the defaults it > > was > 400%. > > I'm not sure what the point of the experiment is? It has to work > with reasonable overead even without --per-thread. > > FWIW Alexey already root caused the problem, so there's no need > to restart the debugging.
Sure; we understand where that overhead is coming from, we have an idea as to how to mitigate that, and we should try to make that work it we can. I was trying to get a feel for how that compares to what we can do today. For other reasons (e.g. fd exhaustion), opening NR_CPUS * n events might not be a great idea on systems with a huge number of CPUs. We might want a heuristic in the perf tool regardless. Thanks, Mark.
