On 05/18/2016 07:06 PM, Rafael J. Wysocki wrote: > On Wed, May 18, 2016 at 2:38 PM, Prarit Bhargava <[email protected]> wrote: >> >> >> On 05/17/2016 08:50 PM, Rafael J. Wysocki wrote: >>> On Tue, May 17, 2016 at 1:34 PM, Prarit Bhargava <[email protected]> wrote: >>>> intel_rapl is currently not supported in virtualized environments. When >>>> booting the warning message >>>> >>>> intel_rapl: no valid rapl domains found in package 0 >>> >>> You seem to be saying that this message is problematic for some >>> reason, so why is it? >>> >> >> I thought about my previous answer and after thinking about it realized I >> didn't >> give you enough background Rafael. Virtual environments won't use this >> feature >> as this is meant for restricting power consumption at the HW level. >> >> So ... here's the situation. Most CPU features from Intel have a CPU feature >> bit (also known in some circles as cpuflags) set for them. For example MCE >> has >> an mce bit that is exposed in /proc/cpuinfo. Unfortunately, for Intel RAPL >> there is no bit (I don't know if someone dropped the ball or if Intel >> intentionally left this feature off ... I've heard both explanations :)). >> >> In any case the Intel RAPL driver is one of the few cpu based drivers in the >> kernel that still does a x86_match_cpu() against supported CPUs. This means >> for >> virtual cpus which export the host cpu's cpu model number, the intel_rapl >> driver >> will attempt to load for each cpu. >> >> As a result the message >> >> intel_rapl: no valid rapl domains found in package 0 >> >> is output as a *visible* error to the user for each virtual core. >> >> The error is valid for native cpus (although over 100s of systems I can say >> I've >> never seen the warning output on a native cpu) but it is clearly not valid >> for >> virtual cpus *because virtualized systems don't use this feature*. >> >> The driver shouldn't load on virt systems. That's the bottom line here, and >> the >> patch prevents that from happening. Would I prefer that there were some >> other >> mechanism to detect RAPL? Yep. I really really would. But beyond mucking >> with >> MSRs (which is definitely more complicated and awful than this simple check) >> I >> don't see any easier method than the one I've proposed. >> >> I really don't want to be the one who sets the precedent of abusing >> x86_hyper in >> this way. I know it isn't the "right" thing to do -- but I honestly do not >> see >> a better or cleaner way out of this. > > One quite obvious alternative might be to reduce the log level of the > message in question, say to pr_debug.
Yeah -- I thought about that too. But that's really a band-aid, isn't it? The code shouldn't execute on virt. P. >
