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

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Date:   Thu, 6 Apr 2023 11:12:16 +0200 (CEST)
From:   Anna-Maria Behnsen <anna-maria@...utronix.de>
To:     Frederic Weisbecker <frederic@...nel.org>
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 v5 16/18] timer: Implement the hierarchical pull model

On Tue, 21 Mar 2023, Frederic Weisbecker wrote:

> On Wed, Mar 01, 2023 at 03:17:42PM +0100, Anna-Maria Behnsen wrote:
> > +static bool tmigr_inactive_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;
> > +
> > +	/* Reset active bit when child is no longer active */
> > +	if (!data->childstate.active)
> > +		newstate.active &= ~(u8)childmask;
> > +
> > +	if (newstate.migrator == (u8)childmask) {
> > +		/*
> > +		 * Find a new migrator for the group, because child group
> > +		 * is idle!
> > +		 */
> > +		if (!data->childstate.active) {
> > +			unsigned long new_migr_bit, active = newstate.active;
> > +
> > +			new_migr_bit = find_first_bit(&active, BIT_CNT);
> > +
> > +			/* Changes need to be propagated */
> > +			walk_done = false;
> 
> Do you need to propagate the changes even if you found a new migrator for the
> group?

No, you shouldn't require the walk then. Will think about it again, fix
(and test) it.

> > +
> > +			if (new_migr_bit != BIT_CNT)
> > +				newstate.migrator = BIT(new_migr_bit);
> > +			else
> > +				newstate.migrator = TMIGR_NONE;
> 
> Thanks.
> 

Thanks,

	Anna-Maria