linux-kernel - Re: [PATCH v4 1/8] tracing: wprobe: Add watchpoint probe event based on hardware breakpoint

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Message-Id: <20250918074248.09cc039bd81ad7ffe2b4b09f@kernel.org>
Date: Thu, 18 Sep 2025 07:42:48 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Randy Dunlap <rdunlap@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>, Peter Zijlstra
 <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, x86@...nel.org,
 Jinchao Wang <wangjinchao600@...il.com>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Thomas Gleixner <tglx@...utronix.de>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "H . Peter Anvin" <hpa@...or.com>, Alexander Shishkin
 <alexander.shishkin@...ux.intel.com>, Ian Rogers <irogers@...gle.com>,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v4 1/8] tracing: wprobe: Add watchpoint probe event
 based on hardware breakpoint

On Wed, 17 Sep 2025 10:13:36 -0700
Randy Dunlap <rdunlap@...radead.org> wrote:

> 
> 
> On 9/17/25 7:38 AM, Masami Hiramatsu (Google) wrote:
> >> +  #           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
> >> +  #              | |         |   |||||     |         |
> >> +           <idle>-0       [000] d.Z1.  717.026259: my_jiffies: (tick_do_update_jiffies64+0xbe/0x130)
> >> +           <idle>-0       [000] d.Z1.  717.026373: my_jiffies: (tick_do_update_jiffies64+0xbe/0x130)
> >> +
> >> +You can see the code which writes to `jiffies` is `do_timer()`.
> > I'm having trouble getting from tick_do_update_jiffies64+0xbe/0x130,
> > which I expect is
> > 	jiffies_64 += ticks;
> > in that function, over to do_timer(), which also updates jiffies_64,
> > but is not called by tick_do_update_jiffies64(). AFAICT, there are
> > no calls to do_timer() in the file (kernel/time/tick-sched.c).
> > 
> > Can you explain, please?
> 
> Let me try this again.
> 
> I understand the stack (call) trace/dump and your explanation, but
> then your next comment says:
> 
> +You can see the code which writes to `jiffies` is `do_timer()`.
> 
> Does that need to be corrected?

Oops! sorry I missed that. Let me fix that.

Thank you for catching!

Thanks,

> 
> thanks.
> -- 
> ~Randy
> 

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