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realtime:documentation:howto:tools:hwlat [2018/07/11 14:55]
ebugden Add description of hwlat tool
realtime:documentation:howto:tools:hwlat [2018/07/13 11:56] (current)
ebugden Update method of clearing trace
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 ====== Ftrace - hwlat tracer ====== ====== Ftrace - hwlat tracer ======
  
-hwlat is an Ftrace tracer designed to detect latencies caused by a system'​s firmware or hardware. The tracer was originally intended for detecting SMIs, but it can detect other low level latencies as well. More details about this tracer can be found in the kernel documentation for Ftrace and for the hardware latency detector.+hwlat is an Ftrace tracer designed to detect latencies caused by a system'​s firmware or hardware. The tracer was originally intended for [[realtime:​documentation:​howto:​debugging:​smi-latency:​start|detecting SMIs]], but it can detect other low level latencies as well. More details about this tracer can be found in the kernel documentation for Ftrace and for the hardware latency detector.
  
 ===== Setup ===== ===== Setup =====
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 ===== Tracing ===== ===== Tracing =====
  
-If the tracer is available, hwlat can be activated manually via tracefs in the same way as any other Ftrace tracer. The following ​few commands ​are written as if they are being run from the root of tracefs (the tracing folder). The '#'​ symbol is used to indicate that the commands must be run as root or with sudo. Here is an example of how to select the hwlat tracer:+If the tracer is available, hwlat can be activated manually via tracefs in the same way as any other Ftrace tracer. The '​[tracing]'​ before the following commands ​is to indicate that they are being run from the root of tracefs (the tracing folder). The '#'​ symbol is used to indicate that the commands must be run as root or with sudo. Here is an example of how to select the hwlat tracer:
  
 <​code>​ <​code>​
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 </​code>​ </​code>​
  
-If another trace is to be taken, the previous ​trace results can be cleared by selecting ​the nop tracer:+If another trace is to be taken, the previous results can be cleared by writing into the trace file:
  
 <​code>​ <​code>​
-[tracing]# echo nop current_tracer+[tracing]# echo > trace
 </​code> ​ </​code> ​
  
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 The kernel documentation for Ftrace and for the hardware latency detector contain details about how to interpret the resulting traces. The kernel documentation for Ftrace and for the hardware latency detector contain details about how to interpret the resulting traces.
 +
 +<WRAP center round todo 60%>
 +Explain how to read the results because the kernel documentation is confusing and/or improve kernel documentation?​
 +</​WRAP>​
 +
realtime/documentation/howto/tools/hwlat.1531320951.txt.gz ยท Last modified: 2018/07/11 14:55 by ebugden