linux-kernel - Re: [PATCH v4 5/5] blktrace: Make init_blk_tracer() asynchronous when trace_async

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Message-Id: <20260130183022.add316050dd9638e6d71a469@kernel.org>
Date: Fri, 30 Jan 2026 18:30:22 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Jens Axboe <axboe@...nel.dk>, Yaxiong Tian <tianyaxiong@...inos.cn>,
 mhiramat@...nel.org, mathieu.desnoyers@...icios.com, corbet@....net,
 skhan@...uxfoundation.org, linux-trace-kernel@...r.kernel.org,
 linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org
Subject: Re: [PATCH v4 5/5] blktrace: Make init_blk_tracer() asynchronous
 when trace_async_init set

On Thu, 29 Jan 2026 15:29:58 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Wed, 28 Jan 2026 19:25:46 -0700
> Jens Axboe <axboe@...nel.dk> wrote:
> 
> > On Jan 28, 2026, at 5:40 PM, Steven Rostedt <rostedt@...dmis.org> 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@...nel.dk>
> 
> 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.
> 
> 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)?

Yeah, for kprobes event case, that sounds good to me. I think [3/5] is
enough to speed it up if user does not define kprobe events on cmdline.

Thank you,

> 
> That is, remove patch 2 and 4 and make this patch always use the work queue.
> 
> -- Steve


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>