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diff --git a/Documentation/hwlat_detector.txt b/Documentation/hwlat_detector.txt deleted file mode 100644 index cb61516..0000000 --- a/Documentation/hwlat_detector.txt +++ /dev/null @@ -1,64 +0,0 @@ -Introduction: -------------- - -The module hwlat_detector is a special purpose kernel module that is used to -detect large system latencies induced by the behavior of certain underlying -hardware or firmware, independent of Linux itself. The code was developed -originally to detect SMIs (System Management Interrupts) on x86 systems, -however there is nothing x86 specific about this patchset. It was -originally written for use by the "RT" patch since the Real Time -kernel is highly latency sensitive. - -SMIs are usually not serviced by the Linux kernel, which typically does not -even know that they are occuring. SMIs are instead are set up by BIOS code -and are serviced by BIOS code, usually for "critical" events such as -management of thermal sensors and fans. Sometimes though, SMIs are used for -other tasks and those tasks can spend an inordinate amount of time in the -handler (sometimes measured in milliseconds). Obviously this is a problem if -you are trying to keep event service latencies down in the microsecond range. - -The hardware latency detector works by hogging all of the cpus for configurable -amounts of time (by calling stop_machine()), polling the CPU Time Stamp Counter -for some period, then looking for gaps in the TSC data. Any gap indicates a -time when the polling was interrupted and since the machine is stopped and -interrupts turned off the only thing that could do that would be an SMI. - -Note that the SMI detector should *NEVER* be used in a production environment. -It is intended to be run manually to determine if the hardware platform has a -problem with long system firmware service routines. - -Usage: ------- - -Loading the module hwlat_detector passing the parameter "enabled=1" (or by -setting the "enable" entry in "hwlat_detector" debugfs toggled on) is the only -step required to start the hwlat_detector. It is possible to redefine the -threshold in microseconds (us) above which latency spikes will be taken -into account (parameter "threshold="). - -Example: - - # modprobe hwlat_detector enabled=1 threshold=100 - -After the module is loaded, it creates a directory named "hwlat_detector" under -the debugfs mountpoint, "/debug/hwlat_detector" for this text. It is necessary -to have debugfs mounted, which might be on /sys/debug on your system. - -The /debug/hwlat_detector interface contains the following files: - -count - number of latency spikes observed since last reset -enable - a global enable/disable toggle (0/1), resets count -max - maximum hardware latency actually observed (usecs) -sample - a pipe from which to read current raw sample data - in the format <timestamp> <latency observed usecs> - (can be opened O_NONBLOCK for a single sample) -threshold - minimum latency value to be considered (usecs) -width - time period to sample with CPUs held (usecs) - must be less than the total window size (enforced) -window - total period of sampling, width being inside (usecs) - -By default we will set width to 500,000 and window to 1,000,000, meaning that -we will sample every 1,000,000 usecs (1s) for 500,000 usecs (0.5s). If we -observe any latencies that exceed the threshold (initially 100 usecs), -then we write to a global sample ring buffer of 8K samples, which is -consumed by reading from the "sample" (pipe) debugfs file interface. |