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

Laurent Riffard
2007-03-02T22:10:05Z

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.
> *