#!/usr/bin/stap
#
# Copyright (C) 2007 Oracle Corp. Chris Mason <chris.mason@oracle.com>
#
# This was implemented to find the most common causes of schedule during
# the AIO io_submit call. It does this by recording which pids are inside
# AIO, and recording the current stack trace if one of those pids is
# inside schedule.
# When the probe exits, it prints out the 30 most common call stacks for
# schedule().
#
# This file is free software. You can redistribute it and/or modify it under
# the terms of the GNU General Public License (GPL); either version 2, or (at
# your option) any later version.
global in_iosubmit
global traces
/*
* add a probe to sys_io_submit, on entry, record in the in_iosubmit
* hash table that this proc is in io_submit
*/
probe syscall.io_submit {
in_iosubmit[tid()] = 1
}
/*
* when we return from sys_io_submit, record that we're no longer there
*/
probe syscall.io_submit.return {
/* this assumes a given proc will do lots of io_submit calls, and
* so doesn't do the more expensive "delete in_iosubmit[p]". If
* there are lots of procs doing small number of io_submit calls,
* the hash may grow pretty big, so using delete may be better
*/
in_iosubmit[tid()] = 0
}
/*
* every time we call schedule, check to see if we started off in
* io_submit. If so, record our backtrace into the traces histogram
*/
probe kernel.function("schedule") {
if (tid() in in_iosubmit) {
traces[backtrace()]++
/*
* change this to if (1) if you want a backtrace every time
* you go into schedule from io_submit. Unfortunately, the traces
* saved into the traces histogram above are truncated to just a
* few lines. so the only way to see the full trace is via the
* more verbose print_backtrace() right here.
*/
if (0) {
printf("schedule in io_submit!\n")
print_backtrace()
}
}
}
/*
* when stap is done (via ctrl-c) go through the record of all the
* trace paths and print the 30 most common.
*/
probe end {
foreach (stack in traces- limit 30) {
printf("%d:", traces[stack])
print_syms(stack);
}
}
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