linux-kernel - Re: [PATCH] Fix optimized search

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Date:	Tue, 20 Nov 2007 23:15:48 -0500
From:	Steven Rostedt <srostedt@...hat.com>
To:	Gregory Haskins <ghaskins@...ell.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Christoph Lameter <clameter@....com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] Fix optimized search

Gregory Haskins wrote:
> I spied a few more issues from http://lkml.org/lkml/2007/11/20/590.
> 
> Patch is below..

Thanks, but I have one update...

> 
> Regards,
> -Greg
> 
> -----------------
> 
> Include cpu 0 in the search, and eliminate the redundant cpu_set since
> the bit should already be set in the mask.
> 
> Signed-off-by: Gregory Haskins <ghaskins@...ell.com>
> ---
> 
>  kernel/sched_rt.c |    7 +++----
>  1 files changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
> index 28feeff..fbf4fb1 100644
> --- a/kernel/sched_rt.c
> +++ b/kernel/sched_rt.c
> @@ -297,7 +297,7 @@ static DEFINE_PER_CPU(cpumask_t, local_cpu_mask);
>  static int find_lowest_cpus(struct task_struct *task, cpumask_t *lowest_mask)
>  {
>  	int       lowest_prio = -1;
> -	int       lowest_cpu  = 0;
> +	int       lowest_cpu  = -1;
>  	int       count       = 0;
>  	int       cpu;
>  
> @@ -319,7 +319,7 @@ static int find_lowest_cpus(struct task_struct *task, cpumask_t *lowest_mask)
>  			 * and the count==1 will cause the algorithm
>  			 * to use the first bit found.
>  			 */
> -			if (lowest_cpu) {
> +			if (lowest_cpu != -1) {
>  				cpus_clear(*lowest_mask);
>  				cpu_set(rq->cpu, *lowest_mask);
>  			}
> @@ -335,7 +335,6 @@ static int find_lowest_cpus(struct task_struct *task, cpumask_t *lowest_mask)
>  				lowest_cpu = cpu;
>  				count = 0;
>  			}
> -			cpu_set(rq->cpu, *lowest_mask);
>  			count++;
>  		} else
>  			cpu_clear(cpu, *lowest_mask);
> @@ -346,7 +345,7 @@ static int find_lowest_cpus(struct task_struct *task, cpumask_t *lowest_mask)
>  	 * runqueues that were of higher prio than
>  	 * the lowest_prio.
>  	 */
> -	if (lowest_cpu) {
> +	if (lowest_cpu != -1) {

We can change this to

   if (lowest_cpu > 0) {

because if lowest_cpu == 0, we don't need to bother with clearing any bits.

I'll apply this next.

Thanks.

-- Steve

>  		/*
>  		 * Perhaps we could add another cpumask op to
>  		 * zero out bits. Like cpu_zero_bits(cpumask, nrbits);
> 

-
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