fio: Introduce the log_entries option

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index 196bca6c0634a9ec624e75a1de7f8cde6ef13414..a3b3acfe712aaf8a287b92647b9fbc2c97b6ebc0 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -3537,6 +3537,18 @@ Measurements and reporting
        :option:`write_bw_log` for details about the filename format and `Log
        File Formats`_ for how data is structured within the file.
 
+.. option:: log_entries=int
+
+       By default, fio will log an entry in the iops, latency, or bw log for
+       every I/O that completes. The initial number of I/O log entries is 1024.
+       When the log entries are all used, new log entries are dynamically
+       allocated.  This dynamic log entry allocation may negatively impact
+       time-related statistics such as I/O tail latencies (e.g. 99.9th percentile
+       completion latency). This option allows specifying a larger initial
+       number of log entries to avoid run-time allocations of new log entries,
+       resulting in more precise time-related I/O statistics.
+       Also see :option:`log_avg_msec`. Defaults to 1024.
+
 .. option:: log_avg_msec=int
 
        By default, fio will log an entry in the iops, latency, or bw log for every