Re: 2.6.21-rc2-mm1: what about CONFIG_NO_HZ and !CONFIG_SMP ?

[Laurent Riffard <laurent.riffard@free.fr>]

Le 02.03.2007 21:57, Siddha, Suresh B a écrit :
> On Fri, Mar 02, 2007 at 10:12:25PM +0100, Laurent Riffard wrote:
>> Le 02.03.2007 12:00, Andrew Morton a écrit :
>>> Temporarily at
>>>
>>>   http://userweb.kernel.org/~akpm/2.6.21-rc2-mm1/
>>>
>>> Will appear later at
>>>
>>>   ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.21-rc2/2.6.21-rc2-mm1/
>> Got this when CONFIG_NO_HZ=y and CONFIG_SMP=n:
>>
>>   CC      kernel/sched.o
>> kernel/sched.c: In function 'trigger_load_balance':
>> kernel/sched.c:3384: error: 'struct rq' has no member named 'in_nohz_recently'
>> kernel/sched.c:3384: error: 'struct rq' has no member named 'idle_at_tick'
>> kernel/sched.c:3385: error: 'struct rq' has no member named 'in_nohz_recently'
>> kernel/sched.c:3387: error: 'nohz' undeclared (first use in this function)
>> kernel/sched.c:3387: error: (Each undeclared identifier is reported only once
>> kernel/sched.c:3387: error: for each function it appears in.)
>> kernel/sched.c:3404: warning: implicit declaration of function 'resched_cpu'
>> kernel/sched.c:3412: error: 'struct rq' has no member named 'idle_at_tick'
>> kernel/sched.c:3422: error: 'struct rq' has no member named 'idle_at_tick'
>> make[1]: *** [kernel/sched.o] Error 1
>> make: *** [kernel] Error 2
>>
>> Looking at kernel/sched.c, it seems CONFIG_NO_HZ should depend on CONFIG_SMP...
> 
> No. There is no such dependency. Can you please check if the below patch fixes
> the compilation issue. Thanks.

Yes, it does fix the compilation issue.

thanks
~~
laurent


> Move trigger_load_balance() under ifdef CONFIG_SMP.
> 
> Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
> ---
> 
> diff -pNru linux-2.6.21-rc2/kernel/sched.c linux-mm/kernel/sched.c
> --- linux-2.6.21-rc2/kernel/sched.c	2007-03-02 13:23:46.000000000 -0800
> +++ linux-mm/kernel/sched.c	2007-03-02 13:26:38.000000000 -0800
> @@ -3156,6 +3156,68 @@ static void run_rebalance_domains(struct
>  	}
>  #endif
>  }
> +
> +/*
> + * Trigger the SCHED_SOFTIRQ if it is time to do periodic load balancing.
> + *
> + * In case of CONFIG_NO_HZ, this is the place where we nominate a new
> + * idle load balancing owner or decide to stop the periodic load balancing,
> + * if the whole system is idle.
> + */
> +static inline void trigger_load_balance(int cpu)
> +{
> +	struct rq *rq = cpu_rq(cpu);
> +#ifdef CONFIG_NO_HZ
> +	/*
> +	 * If we were in the nohz mode recently and busy at the current
> +	 * scheduler tick, then check if we need to nominate new idle
> +	 * load balancer.
> +	 */
> +	if (rq->in_nohz_recently && !rq->idle_at_tick) {
> +		rq->in_nohz_recently = 0;
> +
> +		if (atomic_read(&nohz.load_balancer) == cpu) {
> +			cpu_clear(cpu, nohz.cpu_mask);
> +			atomic_set(&nohz.load_balancer, -1);
> +		}
> +
> +		if (atomic_read(&nohz.load_balancer) == -1) {
> +			/*
> +			 * simple selection for now: Nominate the
> +			 * first cpu in the nohz list to be the next
> +			 * ilb owner.
> +			 *
> +			 * TBD: Traverse the sched domains and nominate
> +			 * the nearest cpu in the nohz.cpu_mask.
> +			 */
> +			int ilb = first_cpu(nohz.cpu_mask);
> +
> +			if (ilb != NR_CPUS)
> +				resched_cpu(ilb);
> +		}
> +	}
> +
> +	/*
> +	 * If this cpu is idle and doing idle load balancing for all the
> +	 * cpus with ticks stopped, is it time for that to stop?
> +	 */
> +	if (rq->idle_at_tick && atomic_read(&nohz.load_balancer) == cpu &&
> +	    cpus_weight(nohz.cpu_mask) == num_online_cpus()) {
> +		resched_cpu(cpu);
> +		return;
> +	}
> +
> +	/*
> +	 * If this cpu is idle and the idle load balancing is done by
> +	 * someone else, then no need raise the SCHED_SOFTIRQ
> +	 */
> +	if (rq->idle_at_tick && atomic_read(&nohz.load_balancer) != cpu &&
> +	    cpu_isset(cpu, nohz.cpu_mask))
> +		return;
> +#endif
> +	if (time_after_eq(jiffies, rq->next_balance))
> +		raise_softirq(SCHED_SOFTIRQ);
> +}
>  #else
>  /*
>   * on UP we do not need to balance between CPUs:
> @@ -3366,68 +3428,6 @@ out_unlock:
>  }
>  
>  /*
> - * Trigger the SCHED_SOFTIRQ if it is time to do periodic load balancing.
> - *
> - * In case of CONFIG_NO_HZ, this is the place where we nominate a new
> - * idle load balancing owner or decide to stop the periodic load balancing,
> - * if the whole system is idle.
> - */
> -static inline void trigger_load_balance(int cpu)
> -{
> -	struct rq *rq = cpu_rq(cpu);
> -#ifdef CONFIG_NO_HZ
> -	/*
> -	 * If we were in the nohz mode recently and busy at the current
> -	 * scheduler tick, then check if we need to nominate new idle
> -	 * load balancer.
> -	 */
> -	if (rq->in_nohz_recently && !rq->idle_at_tick) {
> -		rq->in_nohz_recently = 0;
> -
> -		if (atomic_read(&nohz.load_balancer) == cpu) {
> -			cpu_clear(cpu, nohz.cpu_mask);
> -			atomic_set(&nohz.load_balancer, -1);
> -		}
> -
> -		if (atomic_read(&nohz.load_balancer) == -1) {
> -			/*
> -			 * simple selection for now: Nominate the
> -			 * first cpu in the nohz list to be the next
> -			 * ilb owner.
> -			 *
> -			 * TBD: Traverse the sched domains and nominate
> -			 * the nearest cpu in the nohz.cpu_mask.
> -			 */
> -			int ilb = first_cpu(nohz.cpu_mask);
> -
> -			if (ilb != NR_CPUS)
> -				resched_cpu(ilb);
> -		}
> -	}
> -
> -	/*
> -	 * If this cpu is idle and doing idle load balancing for all the
> -	 * cpus with ticks stopped, is it time for that to stop?
> -	 */
> -	if (rq->idle_at_tick && atomic_read(&nohz.load_balancer) == cpu &&
> -	    cpus_weight(nohz.cpu_mask) == num_online_cpus()) {
> -		resched_cpu(cpu);
> -		return;
> -	}
> -
> -	/*
> -	 * If this cpu is idle and the idle load balancing is done by
> -	 * someone else, then no need raise the SCHED_SOFTIRQ
> -	 */
> -	if (rq->idle_at_tick && atomic_read(&nohz.load_balancer) != cpu &&
> -	    cpu_isset(cpu, nohz.cpu_mask))
> -		return;
> -#endif
> -	if (time_after_eq(jiffies, rq->next_balance))
> -		raise_softirq(SCHED_SOFTIRQ);
> -}
> -
> -/*
>   * This function gets called by the timer code, with HZ frequency.
>   * We call it with interrupts disabled.
>   *