Are these tools (perf, atop, etc) useful and accurate in virtualized environments? For example, under Xen. Fine, I'll say it: on an EC2 or Linode instance. Would there be any skewing or clock issues due to virtualization?
Collecting the comments of HN readers with deep experience in this matter, on this thread, would be preferable to me trying to give a brief and uninformed Google search summary.
Some features of perf will work perfectly in an emulated environment. Perf's kernel tracing uses tracepoints in the kernel (built-in or dynamically patched in), and those will work just fine. However, perf's use of CPU performance counters will only handle those the virtual environment emulates; I don't know if Xen implements those.
Collecting the comments of HN readers with deep experience in this matter, on this thread, would be preferable to me trying to give a brief and uninformed Google search summary.