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Jarkko Sakkinen

Edited 3 months ago

This was pretty cool:

❯ sudo bpftrace -e 'k:tpm_transmit { @start[tid] = nsecs; } kr:tpm_transmit { @[kstack, ustack, comm] = sum(nsecs - @start[tid]); delete(@start[tid]); } END { clear(@start); }'
Attaching 3 probes...
^C

@[
    tpm_transmit_cmd+46
    tpm2_flush_context+120
    tpm2_commit_space+197
    tpm_dev_transmit.constprop.0+137
    tpm_dev_async_work+102
    process_one_work+374
    worker_thread+614
    kthread+207
    ret_from_fork+49
    ret_from_fork_asm+26
, , kworker/4:2]: 2860677
@[
    tpm_dev_transmit.constprop.0+111
    tpm_dev_async_work+102
    process_one_work+374
    worker_thread+614
    kthread+207
    ret_from_fork+49
    ret_from_fork_asm+26
, , kworker/16:1]: 3890693
@[
    tpm_transmit_cmd+46
    tpm2_load_context+195
    tpm2_prepare_space+410
    tpm_dev_transmit.constprop.0+54
    tpm_dev_async_work+102
    process_one_work+374
    worker_thread+614
    kthread+207
    ret_from_fork+49
    ret_from_fork_asm+26
, , kworker/4:2]: 9058524
@[
    tpm_transmit_cmd+46
    tpm2_save_context+179
    tpm2_commit_space+314
    tpm_dev_transmit.constprop.0+137
    tpm_dev_async_work+102
    process_one_work+374
    worker_thread+614
    kthread+207
    ret_from_fork+49
    ret_from_fork_asm+26
, , kworker/4:2]: 11426260
@[
    tpm_transmit_cmd+46
    tpm2_load_context+195
    tpm2_prepare_space+318
    tpm_dev_transmit.constprop.0+54
    tpm_dev_async_work+102
    process_one_work+374
    worker_thread+614
    kthread+207
    ret_from_fork+49
    ret_from_fork_asm+26
, , kworker/4:2]: 14182972
@[
    tpm_transmit_cmd+46
    tpm2_save_context+179
    tpm2_commit_space+155
    tpm_dev_transmit.constprop.0+137
    tpm_dev_async_work+102
    process_one_work+374
    worker_thread+614
    kthread+207
    ret_from_fork+49
    ret_from_fork_asm+26
, , kworker/4:2]: 22597059
@[
    tpm_dev_transmit.constprop.0+111
    tpm_dev_async_work+102
    process_one_work+374
    worker_thread+614
    kthread+207
    ret_from_fork+49
    ret_from_fork_asm+26
, , kworker/4:2]: 1958500581

Gives me total ns time for each possible stack while bpftrace was running :-) Nothing spectacular but I believe this might be enough to get hold of a performance regression:

https://lore.kernel.org/linux-integrity/D43JXBFOOB2O.3U6ZQ7DASR1ZW@kernel.org/

I’m a total beginner with eBPF stuff, and not an expert in tracing and profiling, so any improvement suggestions are welcome.

#linux #kernel #bpftrace

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