Provided by: systemtap-doc_3.1-3ubuntu0.1_all 

NAME
probe::ioscheduler_trace.plug - Fires when a request queue is plugged;
SYNOPSIS
ioscheduler_trace.plug
VALUES
name Name of the probe point rq_queue request queue
DESCRIPTION
ie, requests in the queue cannot be serviced by block driver.
SEE ALSO
tapset::ioscheduler(3stap)