On Wed, 28 Jan 2026 20:51:17 +0800 Yaxiong Tian <[email protected]> wrote:
> On my ARM64 platform, I observed that certain tracing module > initializations run for up to 200ms—for example, init_kprobe_trace(). > Analysis reveals the root cause: the execution flow eval_map_work_func() > →trace_event_update_with_eval_map()→trace_event_update_all() > is highly time-consuming. Although this flow is placed in eval_map_wq > for asynchronous execution, it holds the trace_event_sem lock, causing > other modules to be blocked either directly or indirectly. Also in > init_blk_tracer(), this functions require trace_event_sem device_initcall. > > To resolve this issue, I rename `eval_map_wq` and make it global and moved > other initialization functions under the tracing subsystem that are > related to this lock to run asynchronously on this workqueue. After this > optimization, boot time is reduced by approximately 200ms. > > Given that asynchronous initialization makes it indeterminate when tracing > will begin, we introduce the trace_async_init kernel parameter.Asynchronous > behavior is enabled only when this parameter is explicitly provided. > > Based on my analysis and testing, I've identified that only these two > locations significantly impact timing. Other initcall_* functions do not > exhibit relevant lock contention. > > A brief summary of the test results is as follows: > Before this PATCHS: > [ 0.224933] calling init_kprobe_trace+0x0/0xe0 @ 1 > [ 0.455016] initcall init_kprobe_trace+0x0/0xe0 returned 0 after 230080 > usecs > > Only opt setup_boot_kprobe_events() can see: > [ 0.258609] calling init_blk_tracer+0x0/0x68 @ 1 > [ 0.454991] initcall init_blk_tracer+0x0/0x68 returned 0 after 196377 usecs > > After this PATCHS: > [ 0.224940] calling init_kprobe_trace+0x0/0xe0 @ 1 > [ 0.224946] initcall init_kprobe_trace+0x0/0xe0 returned 0 after 3 usecs > skip -------- > [ 0.264835] calling init_blk_tracer+0x0/0x68 @ 1 > [ 0.264841] initcall init_blk_tracer+0x0/0x68 returned 0 after 2 usecs OK, this series looks good to me. Acked-by: Masami Hiramatsu (Google) <[email protected]> for this series. Thank you, > > --- > Changes in v2: > - Rename eval_map_wq to trace_init_wq. > Changes in v3: > - Opt PATCH 1/3 commit > Changes in v4: > - add trace_async_init boot parameter in patch2 > - add init_kprobe_trace's skip logic in patch3 > - add Suggested-by tag > - Other synchronous optimizations related to trace_async_init > > Yaxiong Tian (5): > tracing: Rename `eval_map_wq` and allow other parts of tracing use it > tracing: add trace_async_init boot parameter > tracing/kprobes: Skip setup_boot_kprobe_events() when no cmdline event > tracing/kprobes: Make setup_boot_kprobe_events() asynchronous when > trace_async_init set > blktrace: Make init_blk_tracer() asynchronous when trace_async_init > set > > .../admin-guide/kernel-parameters.txt | 8 ++++++ > kernel/trace/blktrace.c | 23 +++++++++++++++- > kernel/trace/trace.c | 27 ++++++++++++------- > kernel/trace/trace.h | 2 ++ > kernel/trace/trace_kprobe.c | 18 ++++++++++++- > 5 files changed, 67 insertions(+), 11 deletions(-) > > -- > 2.25.1 > > -- Masami Hiramatsu (Google) <[email protected]>
