* [PATCH 2/2] dynamic configuration for remote rcu callback processing
@ 2006-04-03 20:39 Dimitri Sivanich
2006-05-02 20:58 ` Paul E. McKenney
0 siblings, 1 reply; 2+ messages in thread
From: Dimitri Sivanich @ 2006-04-03 20:39 UTC (permalink / raw)
To: Paul E. McKenney, Dipankar Sarma, linux-kernel; +Cc: mason, Christoph Lameter
This patch add the ability to dynamically configure processors for remote
rcu callback processing. It applies on top of PATCH 1/2.
Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Index: linux/include/linux/rcupdate.h
===================================================================
--- linux.orig/include/linux/rcupdate.h 2006-04-03 15:26:38.743863052 -0500
+++ linux/include/linux/rcupdate.h 2006-04-03 15:26:43.863355795 -0500
@@ -109,6 +109,7 @@ struct rcu_data {
#ifdef CONFIG_SMP
long last_rs_qlen; /* qlen during the last resched */
spinlock_t rmlock; /* for use with remote callback */
+ short batch_stat; /* indicate processing being done */
#endif
};
Index: linux/kernel/rcupdate.c
===================================================================
--- linux.orig/kernel/rcupdate.c 2006-04-03 15:26:38.743863052 -0500
+++ linux/kernel/rcupdate.c 2006-04-03 15:26:43.867355399 -0500
@@ -195,7 +195,7 @@ static int rcu_next_remotercu(void)
/*
* Configure a cpu for remote rcu callback processing.
*/
-static int rcu_set_remote_rcu(int cpu) {
+int rcu_set_remote_rcu(int cpu) {
unsigned long flags;
if (cpu < NR_CPUS) {
@@ -206,11 +206,12 @@ static int rcu_set_remote_rcu(int cpu) {
} else
return 1;
}
+EXPORT_SYMBOL_GPL(rcu_set_remote_rcu);
/*
* Configure a cpu for standard rcu callback processing.
*/
-static void rcu_clear_remote_rcu(int cpu) {
+void rcu_clear_remote_rcu(int cpu) {
unsigned long flags;
if (cpu < NR_CPUS) {
@@ -219,6 +220,7 @@ static void rcu_clear_remote_rcu(int cpu
spin_unlock_irqrestore(&cpu_remotercu_lock, flags);
}
}
+EXPORT_SYMBOL_GPL(rcu_clear_remote_rcu);
/*
* Configure a set of cpus at boot time for remote rcu callback
@@ -238,7 +240,6 @@ static int __init rcu_remotercu_cpu_setu
__setup ("remotercu=", rcu_remotercu_cpu_setup);
#else
-static int rcu_callbacks_processed_remotely(int cpu) { return 0; }
static int rcu_process_remote(int cpu) { return 0; }
static void rcu_clear_remote_rcu(int cpu) {}
#endif
@@ -650,8 +651,16 @@ static void __rcu_process_callbacks(stru
}
rcu_check_quiescent_state(rcp, rdp);
- if (!rcu_callbacks_processed_remotely(cpu) && rdp->donelist)
+#ifdef CONFIG_NUMA
+ if (rdp->donelist && !rcu_callbacks_processed_remotely(cpu) &&
+ (cmpxchg(&rdp->batch_stat, 0, 1)) == 0) {
rcu_do_batch(rdp);
+ rdp->batch_stat = 0;
+ }
+#else
+ if (rdp->donelist)
+ rcu_do_batch(rdp);
+#endif
}
static void rcu_process_callbacks(unsigned long unused)
@@ -692,15 +701,25 @@ static void rcu_process_remote_callbacks
*/
rdp = &per_cpu(rcu_data, cpu);
if (spin_trylock_irq(&rdp->rmlock)) {
- if ((list=xchg(&rdp->donelist, NULL))!=NULL)
- rdp->donetail = &rdp->donelist;
+ /*
+ * batch_stat ensures cpu isn't still running rcu_do_batch.
+ * This can happen if we've just configured on the fly.
+ */
+ if (cmpxchg(&rdp->batch_stat, 0, 2) == 0) {
+ list=xchg(&rdp->donelist, NULL);
+ if (list != NULL)
+ rdp->donetail = &rdp->donelist;
+ }
spin_unlock_irq(&rdp->rmlock);
}
rdp_bh = &per_cpu(rcu_bh_data, cpu);
if (spin_trylock_irq(&rdp_bh->rmlock)) {
- if ((list_bh=xchg(&rdp_bh->donelist, NULL))!=NULL)
- rdp_bh->donetail = &rdp_bh->donelist;
+ if (cmpxchg(&rdp_bh->batch_stat, 0, 2) == 0) {
+ list_bh=xchg(&rdp_bh->donelist, NULL);
+ if (list_bh != NULL)
+ rdp_bh->donetail = &rdp_bh->donelist;
+ }
spin_unlock_irq(&rdp_bh->rmlock);
}
@@ -717,6 +736,8 @@ static void rcu_process_remote_callbacks
old = rdp->qlen;
new = old - cnt;
} while (cmpxchg(&rdp->qlen, old, new)!=old);
+ if (rdp->batch_stat == 2)
+ rdp->batch_stat = 0;
cnt=0;
while (list_bh) {
@@ -729,6 +750,8 @@ static void rcu_process_remote_callbacks
old = rdp_bh->qlen;
new = old - cnt;
} while (cmpxchg(&rdp_bh->qlen, old, new)!=old);
+ if (rdp_bh->batch_stat == 2)
+ rdp_bh->batch_stat = 0;
}
#else
static void rcu_process_remote_callbacks(unsigned long unused) {}
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH 2/2] dynamic configuration for remote rcu callback processing
2006-04-03 20:39 [PATCH 2/2] dynamic configuration for remote rcu callback processing Dimitri Sivanich
@ 2006-05-02 20:58 ` Paul E. McKenney
0 siblings, 0 replies; 2+ messages in thread
From: Paul E. McKenney @ 2006-05-02 20:58 UTC (permalink / raw)
To: Dimitri Sivanich; +Cc: Dipankar Sarma, linux-kernel, mason, Christoph Lameter
On Mon, Apr 03, 2006 at 03:39:58PM -0500, Dimitri Sivanich wrote:
> This patch add the ability to dynamically configure processors for remote
> rcu callback processing. It applies on top of PATCH 1/2.
OK... So the reason some of the races in 1/2 were not a problem is
that that patch did not allow any changes in the group of CPUs that
have their RCU callbacks processed by other CPUs. However, I don't
see how the patch below covers some of them. So I just called them
out in the wrong patch. ;-)
Comments below.
Thanx, Paul
> Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>
> Signed-off-by: Christoph Lameter <clameter@sgi.com>
>
> Index: linux/include/linux/rcupdate.h
> ===================================================================
> --- linux.orig/include/linux/rcupdate.h 2006-04-03 15:26:38.743863052 -0500
> +++ linux/include/linux/rcupdate.h 2006-04-03 15:26:43.863355795 -0500
> @@ -109,6 +109,7 @@ struct rcu_data {
> #ifdef CONFIG_SMP
> long last_rs_qlen; /* qlen during the last resched */
> spinlock_t rmlock; /* for use with remote callback */
> + short batch_stat; /* indicate processing being done */
> #endif
> };
>
> Index: linux/kernel/rcupdate.c
> ===================================================================
> --- linux.orig/kernel/rcupdate.c 2006-04-03 15:26:38.743863052 -0500
> +++ linux/kernel/rcupdate.c 2006-04-03 15:26:43.867355399 -0500
> @@ -195,7 +195,7 @@ static int rcu_next_remotercu(void)
> /*
> * Configure a cpu for remote rcu callback processing.
> */
> -static int rcu_set_remote_rcu(int cpu) {
> +int rcu_set_remote_rcu(int cpu) {
> unsigned long flags;
>
> if (cpu < NR_CPUS) {
> @@ -206,11 +206,12 @@ static int rcu_set_remote_rcu(int cpu) {
> } else
> return 1;
> }
> +EXPORT_SYMBOL_GPL(rcu_set_remote_rcu);
>
> /*
> * Configure a cpu for standard rcu callback processing.
> */
> -static void rcu_clear_remote_rcu(int cpu) {
> +void rcu_clear_remote_rcu(int cpu) {
> unsigned long flags;
>
> if (cpu < NR_CPUS) {
> @@ -219,6 +220,7 @@ static void rcu_clear_remote_rcu(int cpu
> spin_unlock_irqrestore(&cpu_remotercu_lock, flags);
> }
> }
> +EXPORT_SYMBOL_GPL(rcu_clear_remote_rcu);
>
> /*
> * Configure a set of cpus at boot time for remote rcu callback
> @@ -238,7 +240,6 @@ static int __init rcu_remotercu_cpu_setu
>
> __setup ("remotercu=", rcu_remotercu_cpu_setup);
> #else
> -static int rcu_callbacks_processed_remotely(int cpu) { return 0; }
> static int rcu_process_remote(int cpu) { return 0; }
> static void rcu_clear_remote_rcu(int cpu) {}
> #endif
> @@ -650,8 +651,16 @@ static void __rcu_process_callbacks(stru
> }
>
> rcu_check_quiescent_state(rcp, rdp);
> - if (!rcu_callbacks_processed_remotely(cpu) && rdp->donelist)
> +#ifdef CONFIG_NUMA
> + if (rdp->donelist && !rcu_callbacks_processed_remotely(cpu) &&
> + (cmpxchg(&rdp->batch_stat, 0, 1)) == 0) {
I have to ask... Why can't we just use a spinlock here? This code
is effectively using batch_stat as a spinlock, right?
> rcu_do_batch(rdp);
> + rdp->batch_stat = 0;
> + }
> +#else
> + if (rdp->donelist)
> + rcu_do_batch(rdp);
> +#endif
> }
>
> static void rcu_process_callbacks(unsigned long unused)
> @@ -692,15 +701,25 @@ static void rcu_process_remote_callbacks
> */
> rdp = &per_cpu(rcu_data, cpu);
> if (spin_trylock_irq(&rdp->rmlock)) {
> - if ((list=xchg(&rdp->donelist, NULL))!=NULL)
> - rdp->donetail = &rdp->donelist;
> + /*
> + * batch_stat ensures cpu isn't still running rcu_do_batch.
> + * This can happen if we've just configured on the fly.
> + */
> + if (cmpxchg(&rdp->batch_stat, 0, 2) == 0) {
Again, why not just a spinlock? The value 1 vs. 2 does not seem to
be used.
> + list=xchg(&rdp->donelist, NULL);
> + if (list != NULL)
> + rdp->donetail = &rdp->donelist;
> + }
> spin_unlock_irq(&rdp->rmlock);
> }
>
> rdp_bh = &per_cpu(rcu_bh_data, cpu);
> if (spin_trylock_irq(&rdp_bh->rmlock)) {
> - if ((list_bh=xchg(&rdp_bh->donelist, NULL))!=NULL)
> - rdp_bh->donetail = &rdp_bh->donelist;
> + if (cmpxchg(&rdp_bh->batch_stat, 0, 2) == 0) {
> + list_bh=xchg(&rdp_bh->donelist, NULL);
> + if (list_bh != NULL)
> + rdp_bh->donetail = &rdp_bh->donelist;
> + }
> spin_unlock_irq(&rdp_bh->rmlock);
> }
>
> @@ -717,6 +736,8 @@ static void rcu_process_remote_callbacks
> old = rdp->qlen;
> new = old - cnt;
> } while (cmpxchg(&rdp->qlen, old, new)!=old);
> + if (rdp->batch_stat == 2)
> + rdp->batch_stat = 0;
>
> cnt=0;
> while (list_bh) {
> @@ -729,6 +750,8 @@ static void rcu_process_remote_callbacks
> old = rdp_bh->qlen;
> new = old - cnt;
> } while (cmpxchg(&rdp_bh->qlen, old, new)!=old);
> + if (rdp_bh->batch_stat == 2)
> + rdp_bh->batch_stat = 0;
> }
> #else
> static void rcu_process_remote_callbacks(unsigned long unused) {}
^ permalink raw reply [flat|nested] 2+ messages in thread
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