perf record: Enable counters only when kernel is execing subcommand

'perf record' starts counters before subcommand is execed, so
the statistics is not precise because it includes data of some
preparation steps. I fix it with the patch.

In addition, change the condition to fork/exec subcommand. If
there is a subcommand parameter, perf always fork/exec it. The
usage example is:

 # perf record -f -a sleep 10

So this command could collect statistics for 10 seconds
precisely. User still could stop it by CTRL+C. Without the new
capability, user could only input CTRL+C to stop it without
precise time clock.

Signed-off-by: Zhang Yanmin <[email protected]>
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>
Cc: Avi Kivity <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Sheng Yang <[email protected]>
Cc: oerg Roedel <[email protected]>
Cc: Jes Sorensen <[email protected]>
Cc: Marcelo Tosatti <[email protected]>
Cc: Gleb Natapov <[email protected]>
Cc: <[email protected]>
Cc: Zachary Amsden <[email protected]>
LKML-Reference: <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>

0 files changed, 0 insertions, 0 deletions