Lustre 1.6 Operations Manual

Parameter
at_early_margin
at_extra
ldlm_enqueue_min
Description
Sets how far before the deadline Lustre sends an early reply. Default
value is 5 † .
Sets the incremental amount of time that a server asks for with each
early reply. The server does not know how much time the RPC will
take, so it asks for a fixed value. Default value is 30 ‡ . When a server
finds a queued request about to time out (and needs to send an early
reply out), the server adds the at_extra value (up to its estimate). If
the time expires, the Lustre client will enter recovery status and
reconnect to restore it to normal status.
If you see multiple early replies for the same RPC asking for multiple
30-second increases, change the at_extra value to a larger number
to cut down on early replies sent and, therefore, network load.
Sets the minimum lock enqueue time. Default value is 100. The
ldlm_enqueue time is the maximum of the measured enqueue
estimate (influenced by at_min and at_max parameters), multiplied
by a weighting factor, and the ldlm_enqueue_min setting. LDLM
lock enqueues were based on the obd_timeout value; now they
have a dedicated minimum value. Lock enqueues increase as the
measured enqueue times increase (similar to adaptive timeouts).
* In future releases, the default will be 600 (adaptive timeouts will be enabled).
† This default was chosen as a reasonable time in which to send a reply from the point at which it was sent.
‡ This default was chosen as a balance between sending too many early replies for the same RPC and overestimating
the actual completion time.
In Lustre 1.6.5, adaptive timeouts are disabled, by default. 2 To enable adaptive
timeouts, do one of the following:
■ At compile time, rebuild Lustre with:
--enable-adaptive-timeouts
■ At run time, set at_max to 600 on all nodes.
■
$ echo 600 > /sys/module/ptlrpc/at_max
In modprobe.conf, run:
options ptlrpc at_max=600
The modprobe.conf line should be added (s/run/add) on all nodes before Lustre
modules are loaded.
To disable adaptive timeouts, at run time, set at_max to 0 on all nodes.
$ echo 0 > /sys/module/ptlrpc/at_max
2. In Lustre 1.8, adaptive timeouts will be enabled, by default.
Chapter 20 LustreProc 20-7