> Le 09/09/2017 à 20:48, Mateusz Guzik a écrit : On Sun, Sep 10, 2017 at 07:29:11PM +0200, Maxime Villard wrote: > Le 09/09/2017 à 20:48, Mateusz Guzik a écrit : > > [...] > > I installed the 7.1 release, downloaded recent git snapshot and built the > > trunk kernel while using config stolen from the release (had to edit out > > something about 3g modems to make it compile). I presume this is enough > > to not have debug of any sort enabled. > > Not sure I understand; did you test a kernel from the netbsd-7.1 branch, or > from netbsd-current? You might want to test netbsd-current, I know that several > performance-related improvements were made. >
I noted it's a current kernel. The 7.1 release bits were there to ensure I don't run into userspace/kernel debug. > > 3. pmap > > > > It seems most issues stem from slow pmap handling. Chances are there are > > perfectly avoidable shootdowns and in fact cases where there is no need > > to alter KVA in the first place. > > This seems rather surprising to me. I tried to reduce the number of shootdowns > some time ago, but they were already optimized, and my attempts just made them > slower to process. The only related thing I fixed was making sure there is no > kernel page that gets flushed under a local shootdown, but as far as I > remember, it didn't significantly improve performance (on a somewhat old > hardware, I must admit). > Note this was tested on kvm, where shootdowns are more expensive than on bare metal so the result is probably worsened compared to bare-metal (still, kvm is a perfectly fine production vm deployment, so I don't feel bad for testing on it). I'm did not investigate in detail (I'll have to), but I believe dragonflybsd went to extended measures to reduce/eleminate IPIs in general. Most definitely worth looking at. -- Mateusz Guzik Swearing Maintenance Engineer