On Fri, Mar 04, 2016 at 11:19:33AM +0000, Stefan Hajnoczi wrote: > On Thu, Mar 03, 2016 at 02:35:01PM -0500, Luiz Capitulino wrote: > > trace-cmd-server > > ================ > > > > Everything I described could look like this: > > > > # trace-cmd server [ in the host ] > > # trace-cmd record [ in the guest ] > > # trace-cmd report [ in the host, to merge the traces ] > > > > To achieve this, we need two things: > > > > 1. Add an interface to obtain the guest TSC offset from the > > host user-space. > > > > Maybe we could have a new sysfs directory, with a file > > per vCPU thread and the offset as contents? Or maybe > > just add a new entry to /proc/, like: /proc/TID/tsc-offset? > > Yes, the interface is missing. In the past I have heard people using > trace events on the host to: > > 1. Collect tsc offsets > 2. Track which vCPU is scheduled to a host CPU > > So instead of relying on an interface they enable the relevant trace > events on the host and then parse the trace to collect this information. > However, it's a bad solution especially for tsc offsets since you may > wish to trace an already-running VM where the tracepoint that records > the tsc offset may not fire after startup (?). > > Therefore, I agree that an interface for the tsc offset is needed. It seems that KVM still has no such a generic interface to query VM status, right? How about we create one for it? As a start, we can make it fairly simple. Afterward, we can enrich it when necessary. For example: we create this directory to store all KVM guest informations (or general KVM dynamic informations): /sys/hypervisor/kvm/ For each VM, we can have this to store VM specific infos: /sys/hypervisor/kvm/$VM_NAME For each vCPU: /sys/hypervisor/kvm/$VM_NAME/cpus/cpuN/ and we can put tsc-offset here like: /sys/hypervisor/kvm/$VM_NAME/cpus/cpuN/tsc-offset Would this be workable? Thanks. -- peterx -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
