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Date: Fri, 2 Mar 2007 12:57:29 -0800
From: "Siddha, Suresh B" <suresh.b.siddha@...el.com>
To: Laurent Riffard <laurent.riffard@...e.fr>
Cc: "Siddha, Suresh B" <suresh.b.siddha@...el.com>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, Nick Piggin <npiggin@...e.de>
Subject: Re: 2.6.21-rc2-mm1: what about CONFIG_NO_HZ and !CONFIG_SMP ?
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.
---
Move trigger_load_balance() under ifdef CONFIG_SMP.
Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.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.
*
-
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