diff --git a/scst/README b/scst/README index dc1cd0cfb..08aa28fa4 100644 --- a/scst/README +++ b/scst/README @@ -451,8 +451,21 @@ following entries: - measure_latency - whether or not to enable latency measurements. Enabling latency measurements has a small impact on performance but makes detailed information available about how much time is needed - to process SCSI commands. Here is an example of the data produced - by this infrastructure: + to process SCSI commands. The structure of the paths to files with + latency information is as follows: + + /sys/kernel/scst_tgt/targets/${target_driver_name}/${target_port_name}/sessions/${initiator_name}/latency/${io_type}${io_size} + + ${io_type} is n, r, w or b. 'n' means that no data buffer was + associated with the command, 'r' stands for read, 'w' for write + and 'b' for bidirectional. ${io_size} is a power of two between 512 + and 524288. Each file contains statistics for I/O requests with a + size up to ${io_size} and that exceed a smaller I/O size. The files + for ${io_size} 524288 are an exception because these also include + data for all larger requests. + + Here is an example of the data produced by this infrastructure (edited for + clarity): $ echo 1 >/sys/kernel/scst_tgt/measure_latency $ sleep 10 # Wait until an initiator has submitted multiple I/O requests