On Fri, 2007-12-14 at 09:47 +0100, Peter Zijlstra wrote:
> How about something like this:
>
> diff --git a/lib/proportions.c b/lib/proportions.c
> index 332d8c5..4afb330 100644
> --- a/lib/proportions.c
> +++ b/lib/proportions.c
> @@ -190,6 +190,8 @@ prop_adjust_shift(int *pl_shift, unsigned long
> *pl_period, int new_shift)
> * PERCPU
> */
>
> +#define PROP_BATCH (8*(1+ilog2(nr_cpu_ids)))
> +
> int prop_local_init_percpu(struct prop_local_percpu *pl)
> {
> spin_lock_init(&pl->lock);
> @@ -203,6 +205,16 @@ void prop_local_destroy_percpu(struct prop_local_percpu
> *pl)
> percpu_counter_destroy(&pl->events);
> }
>
> +static unsigned long prop_percpu_read(struct prop_local_percpu *pl)
> +{
> + unsigned long val = percpu_counter_read(&pl->events);
> +
> + if (val < (nr_cpu_ids * PROP_BATCH))
> + val = percpu_counter_sum(&pl->events);
> +
> + return val;
> +}
> +
> /*
> * Catch up with missed period expirations.
> *
> @@ -241,7 +253,7 @@ void prop_norm_percpu(struct prop_global *pg, struct
> prop_local_percpu *pl)
> * can never result in a negative number.
> */
> while (pl->period != global_period) {
> - unsigned long val = percpu_counter_read(&pl->events);
> + unsigned long val = prop_percpu_read(pl);
> unsigned long half = (val + 1) >> 1;
>
> /*
> @@ -252,7 +264,7 @@ void prop_norm_percpu(struct prop_global *pg, struct
> prop_local_percpu *pl)
> if (!val)
> break;
>
> - percpu_counter_add(&pl->events, -half);
> + __percpu_counter_add(&pl->events, -half, PROP_BATCH);
> pl->period += period;
> }
> pl->period = global_period;
> @@ -267,7 +279,7 @@ void __prop_inc_percpu(struct prop_descriptor *pd, struct
> prop_local_percpu *pl)
> struct prop_global *pg = prop_get_global(pd);
>
> prop_norm_percpu(pg, pl);
> - percpu_counter_add(&pl->events, 1);
> + __percpu_counter_add(&pl->events, 1, PROP_BATCH);
> percpu_counter_add(&pg->events, 1);
> prop_put_global(pd, pg);
> }
>
Might as well stack something like this on top:
Index: linux-2.6/lib/proportions.c
===================================================================
--- linux-2.6.orig/lib/proportions.c
+++ linux-2.6/lib/proportions.c
@@ -242,31 +242,19 @@ void prop_norm_percpu(struct prop_global
spin_lock_irqsave(&pl->lock, flags);
prop_adjust_shift(&pl->shift, &pl->period, pg->shift);
+
/*
* For each missed period, we half the local counter.
* basically:
* pl->events >> (global_period - pl->period);
- *
- * but since the distributed nature of percpu counters make division
- * rather hard, use a regular subtraction loop. This is safe, because
- * the events will only every be incremented, hence the subtraction
- * can never result in a negative number.
*/
- while (pl->period != global_period) {
- unsigned long val = prop_local_read_percpu(pl);
- unsigned long half = (val + 1) >> 1;
-
- /*
- * Half of zero won't be much less, break out.
- * This limits the loop to shift iterations, even
- * if we missed a million.
- */
- if (!val)
- break;
-
- __percpu_counter_add(&pl->events, -half, PROP_BATCH);
- pl->period += period;
- }
+ period = (global_period - pl->period) >> (pg->shift - 1);
+ if (period < BITS_PER_LONG) {
+ s64 val = (u64)prop_local_read_percpu(pl);
+ __percpu_counter_add(&pl->events, -val + (val >> period),
PROP_BATCH);
+ } else
+ percpu_counter_set(&pl->events, 0);
+
pl->period = global_period;
spin_unlock_irqrestore(&pl->lock, flags);
}
--
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