perf kvm: Add live mode

perf kvm stat currently requires back to back record and report commands
to see stats. e.g,.

  perf kvm stat record -p $pid -- sleep 1
  perf kvm stat report

This is inconvenvient for on box monitoring of a VM. This patch
introduces a 'live' mode that in effect combines the record plus report
into one command. e.g., to monitor a single VM:

  perf kvm stat live -p $pid

or all VMs:

  perf kvm stat live

Same stats options for the record+report path work with the live mode.
Display rate defaults to 1 second and can be changed using the -d
option.

v4:
- address comments from Xiao -- verify_vcpu check should not look at
  processors on line for the host, prune configurable options.
- set attr->{mmap,comm,task} to 0 - don't need task events so trim events
  we have to deal with
- better control of time for queue event flushing to reduce frequency of
  "Timestamp below last timeslice flush" failures.

v3:
updated to use existing tracepoint parsing code

v2:
removed ABSTIME arg from timerfd_settime as mentioned by Namhyung
only call perf_kvm__handle_stdin when poll returns activity.

Signed-off-by: David Ahern <[email protected]>
Reviewed-by: Xiao Guangrong <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Runzhen Wang <[email protected]>
Cc: Xiao Guangrong <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

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