linux-kernel - Re: [PATCH v4 14/16] timer: Implement the hierarchical pull model

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Message-ID: <20221114130937.GG590078@lothringen>
Date:   Mon, 14 Nov 2022 14:09:37 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Anna-Maria Behnsen <anna-maria@...utronix.de>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        John Stultz <jstultz@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Eric Dumazet <edumazet@...gle.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Arjan van de Ven <arjan@...radead.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH v4 14/16] timer: Implement the hierarchical pull model

On Fri, Nov 04, 2022 at 03:57:35PM +0100, Anna-Maria Behnsen wrote:
> +/*
> + * Returns true, if there is nothing to be propagated to the next level
> + *
> + * @data->nextexp is reset to KTIME_MAX; it is reused for first global
> + * event which needs to be handled by migrator (in toplevel group)
> + *
> + * This is the only place where group event expiry value is set.
> + */
> +static bool tmigr_update_events(struct tmigr_group *group,
> +				struct tmigr_group *child,
> +				struct tmigr_walk *data)
> +{
> +	struct tmigr_event *evt, *first_childevt;
> +	bool walk_done;
> +	u64 nextexp;
> +
> +	if (child) {
> +		if (data->childstate.active)
> +			return true;
> +
> +		raw_spin_lock(&child->lock);
> +		raw_spin_lock_nested(&group->lock, SINGLE_DEPTH_NESTING);
> +
> +		first_childevt = tmigr_next_groupevt(child);
> +		nextexp = child->next_expiry;
> +		evt = &child->groupevt;
> +	} else {
> +		nextexp = data->nextexp;
> +
> +		/*
> +		 * Set @data->nextexp to KTIME_MAX; it is reused for first
> +		 * global event which needs to be handled by migrator (in
> +		 * toplevel group)
> +		 */
> +		data->nextexp = KTIME_MAX;
> +
> +		first_childevt = evt = data->evt;
> +		if (test_bit(0, &evt->ignore))

The bit 0 set/clear/test on that ignore field looks a bit confusing.
Is there any reason why it can't be some plain int/boolean?

Thanks.