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Documentation: Add USDT documentation and bpftrace example.

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Add the USDT documentation and a bpftrace example using the
bridge run USDT probes.

Signed-off-by: Eelco Chaudron <echaudro@redhat.com>
Acked-by: Paolo Valerio <pvalerio@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
This commit is contained in:
Eelco Chaudron
2021-12-22 10:17:44 +01:00
committed by Ilya Maximets
parent 512fab8f21
commit ff4c712d45
6 changed files with 399 additions and 6 deletions
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120
utilities/usdt-scripts/bridge_loop.bt Executable file
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#!/usr/bin/env bpftrace
/*
* Copyright (c) 2021 Red Hat, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*
* Script information:
* -------------------
* bridge_loop.bt uses the USDTs in the ovs-vswitchd's main bridge loop
* to report how long it spends running a single loop, as well as the time
* it spends waiting in the poll_loop(). Once done, it will also print a
* histogram for the time spent.
*
* The following is an example of how to use the script on the running
* ovs-vswitchd process:
*
* $ bridge_loop.bt -p `pgrep -n ovs-vswitchd`
* Attaching 4 probes...
* --------------------------------------------------------------
* Tracing ovs-vswitchd's main() loop... Hit Ctrl-C to end.
* --------------------------------------------------------------
* - [886467@ovs-vswitchd] bridge run loop time : 0:00:00.000230706
* - [886467@ovs-vswitchd] poll_block() wait time: 0:00:00.501854292
* - [886467@ovs-vswitchd] bridge run loop time : 0:00:00.000266445
* - [886467@ovs-vswitchd] poll_block() wait time: 0:00:00.499750288
* - [886467@ovs-vswitchd] bridge run loop time : 0:00:00.000254856
* - [886467@ovs-vswitchd] poll_block() wait time: 0:00:00.499944280
* - [886467@ovs-vswitchd] bridge run loop time : 0:00:00.000267390
* - [886467@ovs-vswitchd] poll_block() wait time: 0:00:00.093566288
* - [886467@ovs-vswitchd] bridge run loop time : 0:00:00.000316774
* - [886467@ovs-vswitchd] poll_block() wait time: 0:00:00.406697754
* - [886467@ovs-vswitchd] bridge run loop time : 0:00:00.000264505
* ^C
* --------------------------------------------------------------
* Showing run time histograms in micro seconds:
* --------------------------------------------------------------
*
* @bridge_run_time:
* [0, 1000) 6 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
*
*
* @poll_block_wait_time:
* [90000, 120000) 1 |@@@@@@@@@@@@@@@@@ |
* [120000, 150000) 0 | |
* [150000, 180000) 0 | |
* [180000, 210000) 0 | |
* [210000, 240000) 0 | |
* [240000, 270000) 0 | |
* [270000, 300000) 0 | |
* [300000, 330000) 0 | |
* [330000, 360000) 0 | |
* [360000, 390000) 0 | |
* [390000, 420000) 1 |@@@@@@@@@@@@@@@@@ |
* [420000, 450000) 0 | |
* [450000, 480000) 0 | |
* [480000, 510000) 3 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
*/
BEGIN
{
printf("--------------------------------------------------------------\n");
printf("Tracing ovs-vswitchd's main() loop... Hit Ctrl-C to end.\n");
printf("--------------------------------------------------------------\n");
}
usdt::main:poll_block
{
@pb_start[tid] = nsecs;
if (@rs_start[tid] != 0) {
$delta = nsecs - @rs_start[tid];
printf("- [%d@%s] bridge run loop time : %u:%2.2u:%2.2u.%9.9u\n",
tid, comm,
$delta / 3600 / 1000000000,
$delta / 60 / 1000000000 % 60,
$delta / 1000000000 % 60,
$delta % 1000000000);
@bridge_run_time = lhist($delta / 1000, 0, 1000000, 1000);
}
}
usdt::main:run_start
{
@rs_start[tid] = nsecs;
if (@pb_start[tid] != 0) {
$delta = nsecs - @pb_start[tid];
printf("- [%d@%s] poll_block() wait time: %u:%2.2u:%2.2u.%9.9u\n",
tid, comm,
$delta / 3600 / 1000000000,
$delta / 60 / 1000000000 % 60,
$delta / 1000000000 % 60,
$delta % 1000000000);
@poll_block_wait_time = lhist($delta / 1000, 0, 30000000, 30000);
}
}
END
{
clear(@rs_start);
clear(@pb_start);
printf("\n");
printf("--------------------------------------------------------------\n");
printf("Showing run time histograms in micro seconds:\n");
printf("--------------------------------------------------------------");
}