perf stat: Enable counters when collecting process-wide or system-wide data

Command 'perf stat' doesn't enable counters when collecting an
existing (by -p) process or system-wide statistics. Fix the
issue.

Change the condition of fork/exec subcommand. If there is a
subcommand parameter, perf always forks/execs it. The usage
example is:

 # perf stat -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 use CTRL+C to stop it without
precise time clock.

Another issue is 'perf stat -a' consumes 100% time of a full
single logical cpu. It has a bad impact on running workload.

Fix it by adding a sleep(1) in the while(!done) loop in function
run_perf_stat.

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: Marcelo Tosatti <[email protected]>
Cc: Joerg Roedel <[email protected]>
Cc: Jes Sorensen <[email protected]>
Cc: Gleb Natapov <[email protected]>
Cc: Zachary Amsden <[email protected]>
Cc: <[email protected]>
LKML-Reference: <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>

0 files changed, 0 insertions, 0 deletions