linux-kernel - Re: [PATCH v2 10/20] rv: Add Hybrid Automata monitor type

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Message-ID: <87y0p5sn74.fsf@yellow.woof>
Date: Mon, 20 Oct 2025 15:43:43 +0200
From: Nam Cao <namcao@...utronix.de>
To: Gabriele Monaco <gmonaco@...hat.com>, linux-kernel@...r.kernel.org, Steven
 Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>,
 linux-trace-kernel@...r.kernel.org
Cc: Tomas Glozar <tglozar@...hat.com>, Juri Lelli <jlelli@...hat.com>, Clark
 Williams <williams@...hat.com>, John Kacur <jkacur@...hat.com>
Subject: Re: [PATCH v2 10/20] rv: Add Hybrid Automata monitor type

Gabriele Monaco <gmonaco@...hat.com> writes:
> Alright, that /should/ be possible, provided the value used to set invariants is
> constant or at least doesn't change until we leave the state.
> This seems a fair assumption to make but doesn't stand for the throttle monitor,
> in that case I read the remaining runtime from the dl entity, that one is
> updated frequently, for instance when a task is throttled, it's negative, but
> this doesn't mean the invariant should expect time to be negative.
>
> Runtime is consumed only when a task is running, so here I use an invariant set
> up on the /remaining/ runtime when reaching the running state, that's why also
> switch_in resets the clock (runtime is not replenished, but the runtime_left
> value doesn't need to be subtracted anything).
>
> An alternative would be to have some sort of pause/resume operations on clocks,
> and a task would just pause the clock when preempted, but those operations are
> not backed up by theory and wouldn't really simplify the implementation (use 2
> variables per clock or a single one and some hack to mark it as paused).
>
> Again, there may be better ways, but I found this one the "simplest".
>
> Does it makes sense or am I just crystallising to this implementation?

Ok, now it makes sense.

I have been thinking about this in the past days, and didn't come up
with anything better. Let's leave it be.

Nam