linux-kernel - Re: [patch 4/7] timer: Replace timer base by a cpu index

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Message-ID: <20150527092236.GC2256@linux>
Date:	Wed, 27 May 2015 14:52:36 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Eric Dumazet <edumazet@...gle.com>,
	John Stultz <john.stultz@...aro.org>,
	Joonwoo Park <joonwoop@...eaurora.org>,
	Wenbo Wang <wenbo.wang@...blaze.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Badhri Jagan Sridharan <Badhri@...gle.com>
Subject: Re: [patch 4/7] timer: Replace timer base by a cpu index

On 26-05-15, 22:50, Thomas Gleixner wrote:
>  static struct tvec_base *lock_timer_base(struct timer_list *timer,
>  					unsigned long *flags)
>  	__acquires(timer->base->lock)
>  {
> -	struct tvec_base *base;
> -
>  	for (;;) {
> -		struct tvec_base *prelock_base = timer->base;
> -		base = tbase_get_base(prelock_base);
> -		if (likely(base != NULL)) {
> +		u32 tf = timer->flags;
> +		struct tvec_base *base;
> +
> +		if (!(tf & TIMER_MIGRATING)) {
> +			base = per_cpu_ptr(&tvec_bases, tf & TIMER_CPUMASK);
>  			spin_lock_irqsave(&base->lock, *flags);
> -			if (likely(prelock_base == timer->base))
> +			if (timer->flags == tf)
>  				return base;
> -			/* The timer has migrated to another CPU */

Maybe we should retain this comment. Its helpful for people who aren't
very familiar with timer core.

>  static void migrate_timer_list(struct tvec_base *new_base, struct hlist_head *head)
>  {
>  	struct timer_list *timer;
> +	int cpu = new_base->cpu;
>  
>  	while (!hlist_empty(head)) {
>  		timer = hlist_entry(head->first, struct timer_list, entry);
>  		/* We ignore the accounting on the dying cpu */
>  		detach_timer(timer, false);
> -		timer_set_base(timer, new_base);
> +		timer->flags = (timer->flags & ~TIMER_BASEMASK) | cpu;

Because 'cpu' is used only once in this routine, maybe we can use
'new_base->cpu' here and the line will still be exactly 80 columns
long.

Not sure, but maybe we can create a inline helper for this operation
as it is repeated at multiple places.

Look good otherwise:

Reviewed-by: Viresh Kumar <viresh.kumar@...aro.org>

-- 
viresh
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