[for-next][PATCH 18/34] tracing: Do not call start/stop() functions when tracing_on does not change

From: "Steven Rostedt (VMware)" Currently, when one echo's in 1 into tracing_on, the current tracer's "start()" function is executed, even if tracing_on was already one. This can lead to strange side effects. One being that if the hwlat tracer is enabled, and someone does "echo 1 > tracing_on"

[for-next][PATCH 18/34] tracing: Do not call start/stop() functions when tracing_on does not change

From: "Steven Rostedt (VMware)" Currently, when one echo's in 1 into tracing_on, the current tracer's "start()" function is executed, even if tracing_on was already one. This can lead to strange side effects. One being that if the hwlat tracer is enabled, and someone does "echo 1 > tracing_on"