biostacks.bt

#!/usr/bin/env bpftrace
// biostacks - Show disk I/O latency with initialization stacks.
//
// See BPF Performance Tools, Chapter 9, for an explanation of this tool.
//
// Example of usage:
//
// # ./biostacks.bt
// Attaching 5 probes...
// Tracing block I/O with init stacks. Hit Ctrl-C to end.
// ^C
//
// @usecs[
//     blk_account_io_start+1
//     blk_mq_make_request+1102
//     generic_make_request+292
//     submit_bio+115
//     _xfs_buf_ioapply+798
//     xfs_buf_submit+101
//     xlog_bdstrat+43
//     xlog_sync+705
//     xlog_state_release_iclog+108
//     _xfs_log_force+542
//     xfs_log_force+44
//     xfsaild+428
//     kthread+289
//     ret_from_fork+53
// ]:
// [64K, 128K)            1 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
//
// [...]
//
// @usecs[
//     blk_account_io_start+1
//     blk_mq_make_request+707
//     generic_make_request+292
//     submit_bio+115
//     xfs_add_to_ioend+455
//     xfs_do_writepage+758
//     write_cache_pages+524
//     xfs_vm_writepages+190
//     do_writepages+75
//     __writeback_single_inode+69
//     writeback_sb_inodes+481
//     __writeback_inodes_wb+103
//     wb_writeback+625
//     wb_workfn+384
//     process_one_work+478
//     worker_thread+50
//     kthread+289
//     ret_from_fork+53
// ]:
// [8K, 16K)            560 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
// [16K, 32K)           218 |@@@@@@@@@@@@@@@@@@@@                                |
// [32K, 64K)            26 |@@                                                  |
// [64K, 128K)            2 |                                                    |
// [128K, 256K)          53 |@@@@                                                |
// [256K, 512K)          60 |@@@@@                                               |
//
// This output shows the most frequent stack was XFS writeback, with latencies
// between 8 and 512 microseconds. The other stack included here shows an XFS
// log sync.
//
// Copyright (c) 2019 Brendan Gregg.
// This was originally created for the BPF Performance Tools book
// published by Addison Wesley. ISBN-13: 9780136554820
// When copying or porting, include this comment.

BEGIN
{
  printf("Tracing block I/O with init stacks. Hit Ctrl-C to end.\n");
}

tracepoint:block:block_io_start
{
  $key = (args.dev,args.sector);
  @reqstack[$key] = kstack;
  @reqts[$key] = nsecs;
}

tracepoint:block:block_rq_issue
/@reqts[args.dev,args.sector]/
{
  $key = (args.dev,args.sector);
  @usecs[@reqstack[$key]] = hist(nsecs - @reqts[$key]);
  delete(@reqstack, $key);
  delete(@reqts, $key);
}

END
{
  clear(@reqstack);
  clear(@reqts);
}