linux-kernel - Re: [PATCH 6.1] softirq: Add trace points for tasklet entry/exit

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Message-ID: <2025082257-smirk-backside-6d93@gregkh>
Date: Fri, 22 Aug 2025 15:07:32 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Sumanth Gavini <sumanth.gavini@...oo.com>
Cc: rostedt@...dmis.org, mhiramat@...nel.org, tglx@...utronix.de,
	jstultz@...gle.com, clingutla@...eaurora.org, mingo@...nel.org,
	sashal@...nel.org, boqun.feng@...il.com, ryotkkr98@...il.com,
	kprateek.nayak@....com, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org, "J . Avila" <elavila@...gle.com>
Subject: Re: [PATCH 6.1] softirq: Add trace points for tasklet entry/exit

On Tue, Aug 12, 2025 at 11:17:54AM -0500, Sumanth Gavini wrote:
> commit f4bf3ca2e5cba655824b6e0893a98dfb33ed24e5 upstream.
> 
> Tasklets are supposed to finish their work quickly and should not block the
> current running process, but it is not guaranteed that they do so.
> 
> Currently softirq_entry/exit can be used to analyse the total tasklets
> execution time, but that's not helpful to track individual tasklets
> execution time. That makes it hard to identify tasklet functions, which
> take more time than expected.
> 
> Add tasklet_entry/exit trace point support to track individual tasklet
> execution.
> 
> Trivial usage example:
>    # echo 1 > /sys/kernel/debug/tracing/events/irq/tasklet_entry/enable
>    # echo 1 > /sys/kernel/debug/tracing/events/irq/tasklet_exit/enable
>    # cat /sys/kernel/debug/tracing/trace
>  # tracer: nop
>  #
>  # entries-in-buffer/entries-written: 4/4   #P:4
>  #
>  #                                _-----=> irqs-off/BH-disabled
>  #                               / _----=> need-resched
>  #                              | / _---=> hardirq/softirq
>  #                              || / _--=> preempt-depth
>  #                              ||| / _-=> migrate-disable
>  #                              |||| /     delay
>  #           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
>  #              | |         |   |||||     |         |
>            <idle>-0       [003] ..s1.   314.011428: tasklet_entry: tasklet=0xffffa01ef8db2740 function=tcp_tasklet_func
>            <idle>-0       [003] ..s1.   314.011432: tasklet_exit: tasklet=0xffffa01ef8db2740 function=tcp_tasklet_func
>            <idle>-0       [003] ..s1.   314.017369: tasklet_entry: tasklet=0xffffa01ef8db2740 function=tcp_tasklet_func
>            <idle>-0       [003] ..s1.   314.017371: tasklet_exit: tasklet=0xffffa01ef8db2740 function=tcp_tasklet_func
> 
> Signed-off-by: Lingutla Chandrasekhar <clingutla@...eaurora.org>
> Signed-off-by: J. Avila <elavila@...gle.com>
> Signed-off-by: John Stultz <jstultz@...gle.com>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> Link: https://lore.kernel.org/r/20230407230526.1685443-1-jstultz@google.com
> 
> [elavila: Port to android-mainline]

This is not android-mainline, this is the normal stable tree.

And I'm with John, this makes no sense as to why you need/want these.  I
think that the syzbot report is bogus, sorry.  Please prove me wrong :)

thanks,

greg k-h