Re: [PATCH v5 16/18] timer: Implement the hierarchical pull model

From: Frederic Weisbecker <frederic@kernel.org>
To: Anna-Maria Behnsen <anna-maria@linutronix.de>
Cc: linux-kernel@vger.kernel.org,
	Peter Zijlstra <peterz@infradead.org>,
	John Stultz <jstultz@google.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Eric Dumazet <edumazet@google.com>,
	"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
	Arjan van de Ven <arjan@infradead.org>,
	"Paul E . McKenney" <paulmck@kernel.org>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Rik van Riel <riel@surriel.com>
Subject: Re: [PATCH v5 16/18] timer: Implement the hierarchical pull model
Date: Tue, 14 Mar 2023 14:24:14 +0100	[thread overview]
Message-ID: <ZBB1frBCnpG741ma@localhost.localdomain> (raw)
In-Reply-To: <20230301141744.16063-17-anna-maria@linutronix.de>

Le Wed, Mar 01, 2023 at 03:17:42PM +0100, Anna-Maria Behnsen a écrit :
> diff --git a/kernel/time/timer_migration.c b/kernel/time/timer_migration.c
> new file mode 100644
> index 000000000000..5a600de3623b
> --- /dev/null
> +++ b/kernel/time/timer_migration.c
> +static bool tmigr_active_up(struct tmigr_group *group,
> +			    struct tmigr_group *child,
> +			    void *ptr)
> +{
> +	union tmigr_state curstate, newstate;
> +	struct tmigr_walk *data = ptr;
> +	bool walk_done;
> +	u32 childmask;
> +
> +	childmask = data->childmask;
> +	newstate = curstate = data->groupstate;
> +
> +retry:
> +	walk_done = true;
> +
> +	if (newstate.migrator == TMIGR_NONE) {
> +		newstate.migrator = (u8)childmask;
> +
> +		/* Changes need to be propagated */
> +		walk_done = false;
> +	}
> +
> +	newstate.active |= (u8)childmask;
> +
> +	newstate.seq++;

Are you sure you need this seq counter? What bad scenario can happen without it?

Thanks.
> 