Subject: Re: [patch 1/4] net: percpufy frequently used vars -- add percpu_counter_mod_bh

From: Ravikiran G Thirumalai <[email-masked]>
Date: Wed, 8 Mar 2006 12:26:56 -0800

On Tue, Mar 07, 2006 at 06:13:01PM -0800, Andrew Morton wrote:
> Ravikiran G Thirumalai <[email-masked]> wrote:
> >
> > +static inline void percpu_counter_mod_bh(struct percpu_counter *fbc, long amount)
> >  +{
> >  +	local_bh_disable();
> >  +	percpu_counter_mod(fbc, amount);
> >  +	local_bh_enable();
> >  +}
> >  +
> 
> percpu_counter_mod() does preempt_disable(), which is redundant in this
> context.  So just do fbc->count += amount; here.

OK.  Here is the revised patch.

Add percpu_counter_mod_bh for using these counters safely from
both softirq and process context.

Signed-off by: Pravin B. Shelar <[email-masked]>
Signed-off by: Ravikiran G Thirumalai <[email-masked]>
Signed-off by: Shai Fultheim <[email-masked]>

Index: linux-2.6.16-rc5mm3/include/linux/percpu_counter.h
===================================================================
--- linux-2.6.16-rc5mm3.orig/include/linux/percpu_counter.h	2006-03-07 15:08:00.000000000 -0800
+++ linux-2.6.16-rc5mm3/include/linux/percpu_counter.h	2006-03-08 10:53:13.000000000 -0800
@@ -11,6 +11,7 @@
 #include <linux/smp.h>
 #include <linux/threads.h>
 #include <linux/percpu.h>
+#include <linux/interrupt.h>
 
 #ifdef CONFIG_SMP
 
@@ -40,6 +41,7 @@ static inline void percpu_counter_destro
 
 void percpu_counter_mod(struct percpu_counter *fbc, long amount);
 long percpu_counter_sum(struct percpu_counter *fbc);
+void percpu_counter_mod_bh(struct percpu_counter *fbc, long amount);
 
 static inline long percpu_counter_read(struct percpu_counter *fbc)
 {
@@ -98,6 +100,12 @@ static inline long percpu_counter_sum(st
 	return percpu_counter_read_positive(fbc);
 }
 
+static inline void percpu_counter_mod_bh(struct percpu_counter *fbc, long amount)
+{
+	local_bh_disable();
+	fbc->count += amount;
+	local_bh_enable();
+}
 #endif	/* CONFIG_SMP */
 
 static inline void percpu_counter_inc(struct percpu_counter *fbc)
@@ -110,4 +118,5 @@ static inline void percpu_counter_dec(st
 	percpu_counter_mod(fbc, -1);
 }
 
+
 #endif /* _LINUX_PERCPU_COUNTER_H */
Index: linux-2.6.16-rc5mm3/mm/swap.c
===================================================================
--- linux-2.6.16-rc5mm3.orig/mm/swap.c	2006-03-07 15:08:01.000000000 -0800
+++ linux-2.6.16-rc5mm3/mm/swap.c	2006-03-08 12:11:19.000000000 -0800
@@ -521,11 +521,11 @@ static int cpu_swap_callback(struct noti
 #endif /* CONFIG_SMP */
 
 #ifdef CONFIG_SMP
-void percpu_counter_mod(struct percpu_counter *fbc, long amount)
+static void __percpu_counter_mod(struct percpu_counter *fbc, long amount)
 {
 	long count;
 	long *pcount;
-	int cpu = get_cpu();
+	int cpu = smp_processor_id();
 
 	pcount = per_cpu_ptr(fbc->counters, cpu);
 	count = *pcount + amount;
@@ -537,9 +537,21 @@ void percpu_counter_mod(struct percpu_co
 	} else {
 		*pcount = count;
 	}
-	put_cpu();
 }
-EXPORT_SYMBOL(percpu_counter_mod);
+
+void percpu_counter_mod(struct percpu_counter *fbc, long amount)
+{
+	preempt_disable();
+	__percpu_counter_mod(fbc, amount);
+	preempt_enable();
+}
+
+void percpu_counter_mod_bh(struct percpu_counter *fbc, long amount)
+{
+	local_bh_disable();
+	__percpu_counter_mod(fbc, amount);
+	local_bh_enable();
+}
 
 /*
  * Add up all the per-cpu counts, return the result.  This is a more accurate
@@ -559,6 +571,9 @@ long percpu_counter_sum(struct percpu_co
 	spin_unlock(&fbc->lock);
 	return ret < 0 ? 0 : ret;
 }
+
+EXPORT_SYMBOL(percpu_counter_mod);
+EXPORT_SYMBOL(percpu_counter_mod_bh);
 EXPORT_SYMBOL(percpu_counter_sum);
 #endif