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 <[email protected]>
> Signed-off-by: Christoph Lameter <[email protected]>
>
> 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) {}
-
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