bpftrace MCP Server

Demonstrations of biostacks, the Linux BCC/eBPF version. This tool shows block I/O latency as a histogram, with the kernel stack trace that initiated the I/O. This can help explain disk I/O that is not directly requested by applications (eg, metadata reads on writes, resilvering, etc). For example: # ./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.