Message-ID: <442974BC.30304@cosmosbay.com>
Date: Tue, 28 Mar 2006 19:39:08 +0200
From: Eric Dumazet <dada1@cosmosbay.com>
User-Agent: Thunderbird 1.5 (Windows/20051201)
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To: Dimitri Sivanich <sivanich@sgi.com>
Cc: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org,
       tglx@linutronix.de, mingo@elte.hu, roe@sgi.com, steiner@sgi.com,
       clameter@sgi.com
Subject: Re: [PATCH] Call get_time() only when necessary in run_hrtimer_queue
References: <20060324175136.GA10186@sgi.com> <20060324142849.5cc27edb.akpm@osdl.org> <20060328165127.GC10411@sgi.com>
In-Reply-To: <20060328165127.GC10411@sgi.com>
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Dimitri Sivanich a ?crit :
> 
> The hrtimer work in -mm does improve on the situation, although there
> appears to be some occasional cache line contention for xtime.  The
> following patch (which is similiar to my previously submitted patch)
> is applicable to 2.6.16-mm1 and does take care of at least a good
> portion of that.

I am not sure your patch is correct.

> 
> Index: linux/kernel/hrtimer.c
> ===================================================================
> --- linux.orig/kernel/hrtimer.c	2006-03-27 09:43:40.000000000 -0600
> +++ linux/kernel/hrtimer.c	2006-03-27 12:35:47.416054373 -0600
> @@ -604,14 +604,17 @@ int hrtimer_get_res(const clockid_t whic
>   */
>  static inline void run_hrtimer_queue(struct hrtimer_base *base)
>  {
> -	struct rb_node *node;
> +	struct rb_node *node = base->first;
> +
> +	if (!node)
> +		return;
>  
>  	if (base->get_softirq_time)
>  		base->softirq_time = base->get_softirq_time();
>  
>  	spin_lock_irq(&base->lock);
>  
> -	while ((node = base->first)) {
> +	while (node) {

Are you sure of this change ?

base->first may have changed just before you locked the base->lock 
(spin_lock_irq(&base->lock);)

Eric

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