linux-kernel - Re: [PATCH v5 7/9] rv: Replace tss and sncid monitors with more complete sts

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Message-ID: <20250728155332.sbkepHj7@linutronix.de>
Date: Mon, 28 Jul 2025 17:53:32 +0200
From: Nam Cao <namcao@...utronix.de>
To: Gabriele Monaco <gmonaco@...hat.com>
Cc: linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	Jonathan Corbet <corbet@....net>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	linux-trace-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Tomas Glozar <tglozar@...hat.com>, Juri Lelli <jlelli@...hat.com>,
	Clark Williams <williams@...hat.com>,
	John Kacur <jkacur@...hat.com>
Subject: Re: [PATCH v5 7/9] rv: Replace tss and sncid monitors with more
 complete sts

On Mon, Jul 28, 2025 at 03:50:19PM +0200, Gabriele Monaco wrote:
> The tss monitor currently guarantees task switches can happen only while
> scheduling, whereas the sncid monitor enforces scheduling occurs with
> interrupt disabled.
> 
> Replace the monitors with a more comprehensive specification which
> implies both but also ensures that:
> * each scheduler call disable interrupts to switch
> * each task switch happens with interrupts disabled
> 
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Gabriele Monaco <gmonaco@...hat.com>

I gave this a try on riscv64 and observed some errors:

[  620.696055] rv: monitor sts does not allow event sched_switch on state enable_to_exit
[  621.047705] rv: monitor sts does not allow event sched_switch on state enable_to_exit
[  642.440209] rv: monitor sts does not allow event sched_switch on state enable_to_exit

I tested with two user programs:

    int main() { asm ("unimp"); }
    int main() { asm ("ebreak"); }

The two programs are repeatedly executed:

    #!/bin/bash
    ./test1 &
    ./test2 &
    # ... repeat lots of time

Any idea?

Nam