Re: [PATCH v4 5/5] blktrace: Make init_blk_tracer() asynchronous when trace_async_init set

[Yaxiong Tian]

在 2026/1/30 04:29, Steven Rostedt 写道:
> On Wed, 28 Jan 2026 19:25:46 -0700
> Jens Axboe <axboe@xxxxxxxxx> wrote:
>
> > On Jan 28, 2026, at 5:40 PM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> > > 
> > > Jens,
> > >
> > > Can you give me an acked-by on this patch and I can take the series through
> > > my tree.
> > On phone, hope this works:
> >
> > Acked-by: Jens Axboe <axboe@xxxxxxxxx>
> Thanks!
>
> > > Or perhaps this doesn't even need to test the trace_async_init flag and can
> > > always do the work queue? Does blk_trace ever do tracing at boot up? That
> > > is, before user space starts?
> > Not via the traditonal way of running blktrace.
> Masami and Yaxiong,
>
> I've been thinking about this more and I'm not sure we need the
> trace_async_init kernel parameter at all. As blktrace should only be
> enabled by user space, it can always use the work queue.

Hi Steven and Jens:

I've been thinking about this further. If we need to consider the 
possibility of non-traditional blktrace usage during the boot phase, 
could we perhaps use a grub parameter like 'ftrace=blk' to handle this? 
More specifically, we could check this through 
the|default_bootup_tracer|mechanism.

+bool __init trace_check_need_bootup_tracer(struct tracer *type)
+{
+       if (!default_bootup_tracer)
+               return false;
+
+       if (strncmp(default_bootup_tracer, type->name, MAX_TRACER_SIZE))
+               return false;
+       else
+               return true;
+}
+

> For kprobes, if someone is adding a kprobe on the kernel command line, then
> they are already specifying that tracing is more important.
>
> Patch 3 already keeps kprobes from being an issue with contention of the
> tracing locks, so I don't think it ever needs to use the work queue.
>
> Wouldn't it just be better to remove the trace_async_init and make blktrace
> always use the work queue and kprobes never do it (but exit out early if
> there were no kprobes registered)?
>
> That is, remove patch 2 and 4 and make this patch always use the work queue.
>
> -- Steve