On 05/05/2018 00:15, Peter Zijlstra wrote: > On Fri, May 04, 2018 at 11:44:09PM +0200, Paolo Bonzini wrote: >> On 04/05/2018 12:45, Peter Zijlstra wrote: >>> On Thu, May 03, 2018 at 04:38:23PM +0300, Alexander Shishkin wrote: >>>> On Thu, May 03, 2018 at 02:50:12PM +0200, Paolo Bonzini wrote: >>> >>>>> And you still need the module parameter to decide >>>>> whether the host is _allowed_ to cause incomplete traces in the guest. >>>> >>>> Or rather a parameter to decide who wins in case both host and guest want >>>> to trace the guest. That's arguably better than having different versions of >>>> PT in the guest depending on a module parameter setting. >>> >>> Yes, that sounds like a much better approach. >> >> I don't think so. The possibility that the host would lose tracing data >> just because the guest starts using PT seems hideous to me... > > Well, either way around is a fairly crap situation, the modparam at > least lets the admin pick which it goes. But if you want to always let > the host win, that's fine with me too, less knobs is better. I expect that the default "system-wide" host wins will be used almost always, with "host-guest" being used in case someone actually wants to use PT in guests. I agree that "Host-only, drop guest events" should be removed, since it can be emulated by perf code. Luwei, can you change that? Paolo
