[PATCH] percpu_counter: FBC_BATCH might be too big

[PATCH] percpu_counter: FBC_BATCH might be too big

[Eric Dumazet]

For NR_CPUS >= 16 values, FBC_BATCH is 2*NR_CPUS

Considering more and more distros are using high NR_CPUS values,
it makes sense to use a more sensible value for FBC_BATCH.

A sensible value is 2*num_online_cpus(), with a minimum value of 32
(This minimum value helps branch prediction in __percpu_counter_add())

We already have a hotcpu notifier, so we can adjust FBC_BATCH dynamically.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
---
 include/linux/percpu_counter.h |    6 +-----
 lib/percpu_counter.c           |   14 +++++++++++++-
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
index 9007ccd..c42a184 100644
--- a/include/linux/percpu_counter.h
+++ b/include/linux/percpu_counter.h
@@ -24,11 +24,7 @@ struct percpu_counter {
 	s32 *counters;
 };
 
-#if NR_CPUS >= 16
-#define FBC_BATCH	(NR_CPUS*2)
-#else
-#define FBC_BATCH	(NR_CPUS*4)
-#endif
+extern int FBC_BATCH;
 
 int percpu_counter_init(struct percpu_counter *fbc, s64 amount);
 int percpu_counter_init_irq(struct percpu_counter *fbc, s64 amount);
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index a866389..2fcf943 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -114,6 +114,16 @@ void percpu_counter_destroy(struct percpu_counter *fbc)
 }
 EXPORT_SYMBOL(percpu_counter_destroy);
 
+int FBC_BATCH __read_mostly = 32;
+EXPORT_SYMBOL(FBC_BATCH);
+
+static void compute_batch_value(void)
+{
+	int nr = num_online_cpus();
+
+	FBC_BATCH = max(32, nr*2);
+}
+
 #ifdef CONFIG_HOTPLUG_CPU
 static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
 					unsigned long action, void *hcpu)
@@ -121,6 +131,7 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
 	unsigned int cpu;
 	struct percpu_counter *fbc;
 
+	compute_batch_value();
 	if (action != CPU_DEAD)
 		return NOTIFY_OK;
 
@@ -139,11 +150,12 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
 	mutex_unlock(&percpu_counters_lock);
 	return NOTIFY_OK;
 }
+#endif
 
 static int __init percpu_counter_startup(void)
 {
+	compute_batch_value();
 	hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
 	return 0;
 }
 module_init(percpu_counter_startup);
-#endif

Re: [PATCH] percpu_counter: FBC_BATCH might be too big

[Peter Zijlstra]

On Fri, 2008-12-05 at 17:05 +0100, Eric Dumazet wrote:
> For NR_CPUS >= 16 values, FBC_BATCH is 2*NR_CPUS
> 
> Considering more and more distros are using high NR_CPUS values,
> it makes sense to use a more sensible value for FBC_BATCH.
> 
> A sensible value is 2*num_online_cpus(), with a minimum value of 32
> (This minimum value helps branch prediction in __percpu_counter_add())
> 
> We already have a hotcpu notifier, so we can adjust FBC_BATCH dynamically.

Agreed, that is one of the reasons the proportion code doesn't use the
FBC_BATCH stuff.

Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

> Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
> ---
>  include/linux/percpu_counter.h |    6 +-----
>  lib/percpu_counter.c           |   14 +++++++++++++-
>  2 files changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
> index 9007ccd..c42a184 100644
> --- a/include/linux/percpu_counter.h
> +++ b/include/linux/percpu_counter.h
> @@ -24,11 +24,7 @@ struct percpu_counter {
>  	s32 *counters;
>  };
>  
> -#if NR_CPUS >= 16
> -#define FBC_BATCH	(NR_CPUS*2)
> -#else
> -#define FBC_BATCH	(NR_CPUS*4)
> -#endif
> +extern int FBC_BATCH;
>  
>  int percpu_counter_init(struct percpu_counter *fbc, s64 amount);
>  int percpu_counter_init_irq(struct percpu_counter *fbc, s64 amount);
> diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
> index a866389..2fcf943 100644
> --- a/lib/percpu_counter.c
> +++ b/lib/percpu_counter.c
> @@ -114,6 +114,16 @@ void percpu_counter_destroy(struct percpu_counter *fbc)
>  }
>  EXPORT_SYMBOL(percpu_counter_destroy);
>  
> +int FBC_BATCH __read_mostly = 32;
> +EXPORT_SYMBOL(FBC_BATCH);
> +
> +static void compute_batch_value(void)
> +{
> +	int nr = num_online_cpus();
> +
> +	FBC_BATCH = max(32, nr*2);
> +}
> +
>  #ifdef CONFIG_HOTPLUG_CPU
>  static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
>  					unsigned long action, void *hcpu)
> @@ -121,6 +131,7 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
>  	unsigned int cpu;
>  	struct percpu_counter *fbc;
>  
> +	compute_batch_value();
>  	if (action != CPU_DEAD)
>  		return NOTIFY_OK;
>  
> @@ -139,11 +150,12 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
>  	mutex_unlock(&percpu_counters_lock);
>  	return NOTIFY_OK;
>  }
> +#endif
>  
>  static int __init percpu_counter_startup(void)
>  {
> +	compute_batch_value();
>  	hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
>  	return 0;
>  }
>  module_init(percpu_counter_startup);
> -#endif

Re: [PATCH] percpu_counter: FBC_BATCH might be too big

[David Miller]

From: Eric Dumazet <dada1@cosmosbay.com>
Date: Fri, 05 Dec 2008 17:05:16 +0100

> For NR_CPUS >= 16 values, FBC_BATCH is 2*NR_CPUS
> 
> Considering more and more distros are using high NR_CPUS values,
> it makes sense to use a more sensible value for FBC_BATCH.
> 
> A sensible value is 2*num_online_cpus(), with a minimum value of 32
> (This minimum value helps branch prediction in __percpu_counter_add())
> 
> We already have a hotcpu notifier, so we can adjust FBC_BATCH dynamically.
> 
> Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>

The downside is now we must load this value in these common
routines.  But I think the gain outweights the loss so:

Acked-by: David S. Miller <davem@davemloft.net>

[PATCH, take2] percpu_counter: FBC_BATCH might be too big

[Eric Dumazet]

In this second version I guarded hotcpu_notifier() call by
a #ifdef CONFIG_HOTPLUG_CPU

I wonder why hotcpu_notifier() is not a null op if !CONFIG_HOTPLUG_CPU

Thank you

[PATCH] percpu_counter: FBC_BATCH might be too big

For NR_CPUS >= 16 values, FBC_BATCH is 2*NR_CPUS

Considering more and more distros are using high NR_CPUS values,
it makes sense to use a more sensible value for FBC_BATCH.

A sensible value is 2*num_online_cpus(), with a minimum value of 32
(This minimum value helps branch prediction in __percpu_counter_add())

We already have a hotcpu notifier, so we can adjust FBC_BATCH dynamically.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
 include/linux/percpu_counter.h |    6 +-----
 lib/percpu_counter.c           |   16 +++++++++++++++-
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
index 9007ccd..c42a184 100644
--- a/include/linux/percpu_counter.h
+++ b/include/linux/percpu_counter.h
@@ -24,11 +24,7 @@ struct percpu_counter {
 	s32 *counters;
 };
 
-#if NR_CPUS >= 16
-#define FBC_BATCH	(NR_CPUS*2)
-#else
-#define FBC_BATCH	(NR_CPUS*4)
-#endif
+extern int FBC_BATCH;
 
 int percpu_counter_init(struct percpu_counter *fbc, s64 amount);
 int percpu_counter_init_irq(struct percpu_counter *fbc, s64 amount);
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index a866389..e21ce7c 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -114,6 +114,16 @@ void percpu_counter_destroy(struct percpu_counter *fbc)
 }
 EXPORT_SYMBOL(percpu_counter_destroy);
 
+int FBC_BATCH __read_mostly = 32;
+EXPORT_SYMBOL(FBC_BATCH);
+
+static void compute_batch_value(void)
+{
+	int nr = num_online_cpus();
+
+	FBC_BATCH = max(32, nr*2);
+}
+
 #ifdef CONFIG_HOTPLUG_CPU
 static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
 					unsigned long action, void *hcpu)
@@ -121,6 +131,7 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
 	unsigned int cpu;
 	struct percpu_counter *fbc;
 
+	compute_batch_value();
 	if (action != CPU_DEAD)
 		return NOTIFY_OK;
 
@@ -139,11 +150,14 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
 	mutex_unlock(&percpu_counters_lock);
 	return NOTIFY_OK;
 }
+#endif
 
 static int __init percpu_counter_startup(void)
 {
+	compute_batch_value();
+#ifdef CONFIG_HOTPLUG_CPU
 	hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
+#endif
 	return 0;
 }
 module_init(percpu_counter_startup);
-#endif

Re: [PATCH, take2] percpu_counter: FBC_BATCH might be too big

[Andrew Morton]

On Sun, 07 Dec 2008 10:25:45 +0100 Eric Dumazet <dada1@cosmosbay.com> wrote:

> In this second version I guarded hotcpu_notifier() call by
> a #ifdef CONFIG_HOTPLUG_CPU
> 
> I wonder why hotcpu_notifier() is not a null op if !CONFIG_HOTPLUG_CPU
> 
> Thank you
> 
> [PATCH] percpu_counter: FBC_BATCH might be too big
> 
> For NR_CPUS >= 16 values, FBC_BATCH is 2*NR_CPUS
> 
> Considering more and more distros are using high NR_CPUS values,
> it makes sense to use a more sensible value for FBC_BATCH.
> 
> A sensible value is 2*num_online_cpus(), with a minimum value of 32
> (This minimum value helps branch prediction in __percpu_counter_add())
> 
> We already have a hotcpu notifier, so we can adjust FBC_BATCH dynamically.

Yup, anything using NR_CPUS is probably wrong.

> diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
> index 9007ccd..c42a184 100644
> --- a/include/linux/percpu_counter.h
> +++ b/include/linux/percpu_counter.h
> @@ -24,11 +24,7 @@ struct percpu_counter {
>  	s32 *counters;
>  };
>  
> -#if NR_CPUS >= 16
> -#define FBC_BATCH	(NR_CPUS*2)
> -#else
> -#define FBC_BATCH	(NR_CPUS*4)
> -#endif
> +extern int FBC_BATCH;

y:/usr/src/linux-2.6.28-rc7> grep -r FBC_BATCH . | wc -l
7

Can we fix this properly please?  It should now become lower case, and
it was a pretty dopey name anyway - now would be a good time to improve
it. `percpu_counter_batch'?

>  int percpu_counter_init(struct percpu_counter *fbc, s64 amount);
>  int percpu_counter_init_irq(struct percpu_counter *fbc, s64 amount);
> diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
> index a866389..e21ce7c 100644
> --- a/lib/percpu_counter.c
> +++ b/lib/percpu_counter.c
> @@ -114,6 +114,16 @@ void percpu_counter_destroy(struct percpu_counter *fbc)
>  }
>  EXPORT_SYMBOL(percpu_counter_destroy);
>  
> +int FBC_BATCH __read_mostly = 32;
> +EXPORT_SYMBOL(FBC_BATCH);
> +
> +static void compute_batch_value(void)
> +{
> +	int nr = num_online_cpus();
> +
> +	FBC_BATCH = max(32, nr*2);
> +}
> +
>  #ifdef CONFIG_HOTPLUG_CPU
>  static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
>  					unsigned long action, void *hcpu)
> @@ -121,6 +131,7 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
>  	unsigned int cpu;
>  	struct percpu_counter *fbc;
>  
> +	compute_batch_value();
>  	if (action != CPU_DEAD)
>  		return NOTIFY_OK;
>  
> @@ -139,11 +150,14 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
>  	mutex_unlock(&percpu_counters_lock);
>  	return NOTIFY_OK;
>  }
> +#endif
>  
>  static int __init percpu_counter_startup(void)
>  {
> +	compute_batch_value();
> +#ifdef CONFIG_HOTPLUG_CPU
>  	hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
> +#endif
>  	return 0;
>  }
>  module_init(percpu_counter_startup);
> -#endif

hm, now what's going on in there?  We should be able to drop the #ifdef
CONFIG_HOTPLUG_CPU from lib/percpu_counter.c altogether. 
hotcpu_notifier() will do the right thing, and the compiler should
generate no code for percpu_counter_hotcpu_callback() if
CONFIG_HOTPLUG_CPU=n.  

Do

	$EDITOR  $(grep -l hotcpu_notifier */*.c)

and you'll see lots of code gets it right, and lots of code gets it wrong.

Re: [PATCH, take2] percpu_counter: FBC_BATCH might be too big

[Eric Dumazet]

Andrew Morton a écrit :
> On Sun, 07 Dec 2008 10:25:45 +0100 Eric Dumazet <dada1@cosmosbay.com> wrote:
> 
>> In this second version I guarded hotcpu_notifier() call by
>> a #ifdef CONFIG_HOTPLUG_CPU
>>
>> I wonder why hotcpu_notifier() is not a null op if !CONFIG_HOTPLUG_CPU
>>
>> Thank you
>>
>> [PATCH] percpu_counter: FBC_BATCH might be too big
>>
>> For NR_CPUS >= 16 values, FBC_BATCH is 2*NR_CPUS
>>
>> Considering more and more distros are using high NR_CPUS values,
>> it makes sense to use a more sensible value for FBC_BATCH.
>>
>> A sensible value is 2*num_online_cpus(), with a minimum value of 32
>> (This minimum value helps branch prediction in __percpu_counter_add())
>>
>> We already have a hotcpu notifier, so we can adjust FBC_BATCH dynamically.
> 
> Yup, anything using NR_CPUS is probably wrong.
> 
>> diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
>> index 9007ccd..c42a184 100644
>> --- a/include/linux/percpu_counter.h
>> +++ b/include/linux/percpu_counter.h
>> @@ -24,11 +24,7 @@ struct percpu_counter {
>>  	s32 *counters;
>>  };
>>  
>> -#if NR_CPUS >= 16
>> -#define FBC_BATCH	(NR_CPUS*2)
>> -#else
>> -#define FBC_BATCH	(NR_CPUS*4)
>> -#endif
>> +extern int FBC_BATCH;
> 
> y:/usr/src/linux-2.6.28-rc7> grep -r FBC_BATCH . | wc -l
> 7
> 
> Can we fix this properly please?  It should now become lower case, and
> it was a pretty dopey name anyway - now would be a good time to improve
> it. `percpu_counter_batch'?

Yes

> 
>>  int percpu_counter_init(struct percpu_counter *fbc, s64 amount);
>>  int percpu_counter_init_irq(struct percpu_counter *fbc, s64 amount);
>> diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
>> index a866389..e21ce7c 100644
>> --- a/lib/percpu_counter.c
>> +++ b/lib/percpu_counter.c
>> @@ -114,6 +114,16 @@ void percpu_counter_destroy(struct percpu_counter *fbc)
>>  }
>>  EXPORT_SYMBOL(percpu_counter_destroy);
>>  
>> +int FBC_BATCH __read_mostly = 32;
>> +EXPORT_SYMBOL(FBC_BATCH);
>> +
>> +static void compute_batch_value(void)
>> +{
>> +	int nr = num_online_cpus();
>> +
>> +	FBC_BATCH = max(32, nr*2);
>> +}
>> +
>>  #ifdef CONFIG_HOTPLUG_CPU
>>  static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
>>  					unsigned long action, void *hcpu)
>> @@ -121,6 +131,7 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
>>  	unsigned int cpu;
>>  	struct percpu_counter *fbc;
>>  
>> +	compute_batch_value();
>>  	if (action != CPU_DEAD)
>>  		return NOTIFY_OK;
>>  
>> @@ -139,11 +150,14 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
>>  	mutex_unlock(&percpu_counters_lock);
>>  	return NOTIFY_OK;
>>  }
>> +#endif
>>  
>>  static int __init percpu_counter_startup(void)
>>  {
>> +	compute_batch_value();
>> +#ifdef CONFIG_HOTPLUG_CPU
>>  	hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
>> +#endif
>>  	return 0;
>>  }
>>  module_init(percpu_counter_startup);
>> -#endif
> 
> hm, now what's going on in there?  We should be able to drop the #ifdef
> CONFIG_HOTPLUG_CPU from lib/percpu_counter.c altogether. 
> hotcpu_notifier() will do the right thing, and the compiler should
> generate no code for percpu_counter_hotcpu_callback() if
> CONFIG_HOTPLUG_CPU=n.  
> 
> Do
> 
> 	$EDITOR  $(grep -l hotcpu_notifier */*.c)
> 
> and you'll see lots of code gets it right, and lots of code gets it wrong.

I see nothing interesting, I must be blind.

lib/percpu_counter.c: In function 'percpu_counter_startup':
lib/percpu_counter.c:158: error: 'percpu_counter_hotcpu_callback' undeclared (first use in this function)
lib/percpu_counter.c:158: error: (Each undeclared identifier is reported only once
lib/percpu_counter.c:158: error: for each function it appears in.)
make[1]: *** [lib/percpu_counter.o] Error 1

static int __init percpu_counter_startup(void)
{
        compute_batch_value();
        hotcpu_notifier(percpu_counter_hotcpu_callback, 0); << ERROR >>
        return 0;
}
module_init(percpu_counter_startup);

# grep hotcpu_notifier include/linux/cpu.h
#define hotcpu_notifier(fn, pri) {                          \
#define hotcpu_notifier(fn, pri)    do { (void)(fn); } while (0)  << ERROR >>


If changed to :

static struct notifier_block __cpuinitdata percpu_counter_cpu_notifier = {
        .notifier_call  = percpu_counter_hotcpu_callback,
};
static int __init percpu_counter_startup(void)
{
        compute_batch_value();
        register_hotcpu_notifier(&percpu_counter_cpu_notifier);
        return 0;
}
module_init(percpu_counter_startup);

Then error is :
lib/percpu_counter.c:156: error: 'percpu_counter_hotcpu_callback' undeclared here (not in a function)
make[1]: *** [lib/percpu_counter.o] Error 1


So the only way seems to add an ugly

#define percpu_counter_hotcpu_callback NULL

Is is what you name "the right thing" ?

Thanks

[PATCH] percpu_counter: FBC_BATCH should be a variable

For NR_CPUS >= 16 values, FBC_BATCH is 2*NR_CPUS

Considering more and more distros are using high NR_CPUS values,
it makes sense to use a more sensible value for FBC_BATCH.

A sensible value is 2*num_online_cpus(), with a minimum value of 32
(This minimum value helps branch prediction in __percpu_counter_add())

We already have a hotcpu notifier, so we can adjust FBC_BATCH dynamically.

We rename FBC_BATCH to percpu_counter_batch since its not a constant
anymore.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
 fs/ext4/ext4.h                 |    6 +++---
 fs/ext4/inode.c                |    2 +-
 include/linux/percpu_counter.h |    8 ++------
 lib/percpu_counter.c           |   16 +++++++++++++++-
 4 files changed, 21 insertions(+), 11 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index b0537c8..6c46c64 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1225,11 +1225,11 @@ do {								\
 } while (0)
 
 #ifdef CONFIG_SMP
-/* Each CPU can accumulate FBC_BATCH blocks in their local
+/* Each CPU can accumulate percpu_counter_batch blocks in their local
  * counters. So we need to make sure we have free blocks more
- * than FBC_BATCH  * nr_cpu_ids. Also add a window of 4 times.
+ * than percpu_counter_batch  * nr_cpu_ids. Also add a window of 4 times.
  */
-#define EXT4_FREEBLOCKS_WATERMARK (4 * (FBC_BATCH * nr_cpu_ids))
+#define EXT4_FREEBLOCKS_WATERMARK (4 * (percpu_counter_batch * nr_cpu_ids))
 #else
 #define EXT4_FREEBLOCKS_WATERMARK 0
 #endif
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index be21a5a..db661e7 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2497,7 +2497,7 @@ static int ext4_nonda_switch(struct super_block *sb)
 	/*
 	 * switch to non delalloc mode if we are running low
 	 * on free block. The free block accounting via percpu
-	 * counters can get slightly wrong with FBC_BATCH getting
+	 * counters can get slightly wrong with percpu_counter_batch getting
 	 * accumulated on each CPU without updating global counters
 	 * Delalloc need an accurate free block accounting. So switch
 	 * to non delalloc when we are near to error range.
diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
index 9007ccd..99de7a3 100644
--- a/include/linux/percpu_counter.h
+++ b/include/linux/percpu_counter.h
@@ -24,11 +24,7 @@ struct percpu_counter {
 	s32 *counters;
 };
 
-#if NR_CPUS >= 16
-#define FBC_BATCH	(NR_CPUS*2)
-#else
-#define FBC_BATCH	(NR_CPUS*4)
-#endif
+extern int percpu_counter_batch;
 
 int percpu_counter_init(struct percpu_counter *fbc, s64 amount);
 int percpu_counter_init_irq(struct percpu_counter *fbc, s64 amount);
@@ -39,7 +35,7 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc);
 
 static inline void percpu_counter_add(struct percpu_counter *fbc, s64 amount)
 {
-	__percpu_counter_add(fbc, amount, FBC_BATCH);
+	__percpu_counter_add(fbc, amount, percpu_counter_batch);
 }
 
 static inline s64 percpu_counter_sum_positive(struct percpu_counter *fbc)
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index a866389..519b877 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -114,6 +114,16 @@ void percpu_counter_destroy(struct percpu_counter *fbc)
 }
 EXPORT_SYMBOL(percpu_counter_destroy);
 
+int percpu_counter_batch __read_mostly = 32;
+EXPORT_SYMBOL(percpu_counter_batch);
+
+static void compute_batch_value(void)
+{
+	int nr = num_online_cpus();
+
+	percpu_counter_batch = max(32, nr*2);
+}
+
 #ifdef CONFIG_HOTPLUG_CPU
 static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
 					unsigned long action, void *hcpu)
@@ -121,6 +131,7 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
 	unsigned int cpu;
 	struct percpu_counter *fbc;
 
+	compute_batch_value();
 	if (action != CPU_DEAD)
 		return NOTIFY_OK;
 
@@ -139,11 +150,14 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
 	mutex_unlock(&percpu_counters_lock);
 	return NOTIFY_OK;
 }
+#else
+#define percpu_counter_hotcpu_callback NULL
+#endif /* CONFIG_HOTPLUG_CPU */
 
 static int __init percpu_counter_startup(void)
 {
+	compute_batch_value();
 	hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
 	return 0;
 }
 module_init(percpu_counter_startup);
-#endif

--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH, take2] percpu_counter: FBC_BATCH might be too big

[Andrew Morton]

On Sun, 07 Dec 2008 19:30:10 +0100 Eric Dumazet <dada1@cosmosbay.com> wrote:

> > 
> > Do
> > 
> > 	$EDITOR  $(grep -l hotcpu_notifier */*.c)
> > 
> > and you'll see lots of code gets it right, and lots of code gets it wrong.
> 
> I see nothing interesting, I must be blind.
> 
> lib/percpu_counter.c: In function 'percpu_counter_startup':
> lib/percpu_counter.c:158: error: 'percpu_counter_hotcpu_callback' undeclared (first use in this function)
> lib/percpu_counter.c:158: error: (Each undeclared identifier is reported only once
> lib/percpu_counter.c:158: error: for each function it appears in.)
> make[1]: *** [lib/percpu_counter.o] Error 1

Perhaps you still had percpu_counter_hotcpu_callback inside #ifdef.

That a look at kernel/workqueue.c, fs/buffer.c.  No #ifdef CONFIG_HOTPLUG_CPU
needed at all.

[PATCH] percpu_counter: FBC_BATCH should be a variable

[Eric Dumazet]

Andrew Morton a écrit :
> On Sun, 07 Dec 2008 19:30:10 +0100 Eric Dumazet <dada1@cosmosbay.com> wrote:
> 
>>> Do
>>>
>>> 	$EDITOR  $(grep -l hotcpu_notifier */*.c)
>>>
>>> and you'll see lots of code gets it right, and lots of code gets it wrong.
>> I see nothing interesting, I must be blind.
>>
>> lib/percpu_counter.c: In function 'percpu_counter_startup':
>> lib/percpu_counter.c:158: error: 'percpu_counter_hotcpu_callback' undeclared (first use in this function)
>> lib/percpu_counter.c:158: error: (Each undeclared identifier is reported only once
>> lib/percpu_counter.c:158: error: for each function it appears in.)
>> make[1]: *** [lib/percpu_counter.o] Error 1
> 
> Perhaps you still had percpu_counter_hotcpu_callback inside #ifdef.
> 
> That a look at kernel/workqueue.c, fs/buffer.c.  No #ifdef CONFIG_HOTPLUG_CPU
> needed at all.

We still need some #ifdef or we also must also delete them around "struct list_head list"
in include/linux/percpu_counter.h and grow struct percpu_counter.

lib/percpu_counter.c: In function 'percpu_counter_hotcpu_callback':
lib/percpu_counter.c:137: error: 'struct percpu_counter' has no member named 'list'
lib/percpu_counter.c:137: warning: type defaults to 'int' in declaration of '__mptr'
lib/percpu_counter.c:137: warning: initialization from incompatible pointer type
...


Thank you Andrew


[PATCH] percpu_counter: FBC_BATCH should be a variable

For NR_CPUS >= 16 values, FBC_BATCH is 2*NR_CPUS

Considering more and more distros are using high NR_CPUS values,
it makes sense to use a more sensible value for FBC_BATCH, and
get rid of NR_CPUS.

A sensible value is 2*num_online_cpus(), with a minimum value of 32
(This minimum value helps branch prediction in __percpu_counter_add())

We already have a hotcpu notifier, so we can adjust FBC_BATCH dynamically.

We rename FBC_BATCH to percpu_counter_batch since its not a constant
anymore.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
 fs/ext4/ext4.h                 |    6 +++---
 fs/ext4/inode.c                |    2 +-
 include/linux/percpu_counter.h |    8 ++------
 lib/percpu_counter.c           |   18 ++++++++++++++----
 4 files changed, 20 insertions(+), 14 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index b0537c8..6c46c64 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1225,11 +1225,11 @@ do {								\
 } while (0)
 
 #ifdef CONFIG_SMP
-/* Each CPU can accumulate FBC_BATCH blocks in their local
+/* Each CPU can accumulate percpu_counter_batch blocks in their local
  * counters. So we need to make sure we have free blocks more
- * than FBC_BATCH  * nr_cpu_ids. Also add a window of 4 times.
+ * than percpu_counter_batch  * nr_cpu_ids. Also add a window of 4 times.
  */
-#define EXT4_FREEBLOCKS_WATERMARK (4 * (FBC_BATCH * nr_cpu_ids))
+#define EXT4_FREEBLOCKS_WATERMARK (4 * (percpu_counter_batch * nr_cpu_ids))
 #else
 #define EXT4_FREEBLOCKS_WATERMARK 0
 #endif
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index be21a5a..db661e7 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2497,7 +2497,7 @@ static int ext4_nonda_switch(struct super_block *sb)
 	/*
 	 * switch to non delalloc mode if we are running low
 	 * on free block. The free block accounting via percpu
-	 * counters can get slightly wrong with FBC_BATCH getting
+	 * counters can get slightly wrong with percpu_counter_batch getting
 	 * accumulated on each CPU without updating global counters
 	 * Delalloc need an accurate free block accounting. So switch
 	 * to non delalloc when we are near to error range.
diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
index 9007ccd..99de7a3 100644
--- a/include/linux/percpu_counter.h
+++ b/include/linux/percpu_counter.h
@@ -24,11 +24,7 @@ struct percpu_counter {
 	s32 *counters;
 };
 
-#if NR_CPUS >= 16
-#define FBC_BATCH	(NR_CPUS*2)
-#else
-#define FBC_BATCH	(NR_CPUS*4)
-#endif
+extern int percpu_counter_batch;
 
 int percpu_counter_init(struct percpu_counter *fbc, s64 amount);
 int percpu_counter_init_irq(struct percpu_counter *fbc, s64 amount);
@@ -39,7 +35,7 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc);
 
 static inline void percpu_counter_add(struct percpu_counter *fbc, s64 amount)
 {
-	__percpu_counter_add(fbc, amount, FBC_BATCH);
+	__percpu_counter_add(fbc, amount, percpu_counter_batch);
 }
 
 static inline s64 percpu_counter_sum_positive(struct percpu_counter *fbc)
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index a866389..e73eb5b 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -9,10 +9,8 @@
 #include <linux/cpu.h>
 #include <linux/module.h>
 
-#ifdef CONFIG_HOTPLUG_CPU
 static LIST_HEAD(percpu_counters);
 static DEFINE_MUTEX(percpu_counters_lock);
-#endif
 
 void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
 {
@@ -114,13 +112,24 @@ void percpu_counter_destroy(struct percpu_counter *fbc)
 }
 EXPORT_SYMBOL(percpu_counter_destroy);
 
-#ifdef CONFIG_HOTPLUG_CPU
+int percpu_counter_batch __read_mostly = 32;
+EXPORT_SYMBOL(percpu_counter_batch);
+
+static void compute_batch_value(void)
+{
+	int nr = num_online_cpus();
+
+	percpu_counter_batch = max(32, nr*2);
+}
+
 static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
 					unsigned long action, void *hcpu)
 {
+#ifdef CONFIG_HOTPLUG_CPU
 	unsigned int cpu;
 	struct percpu_counter *fbc;
 
+	compute_batch_value();
 	if (action != CPU_DEAD)
 		return NOTIFY_OK;
 
@@ -137,13 +146,14 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
 		spin_unlock_irqrestore(&fbc->lock, flags);
 	}
 	mutex_unlock(&percpu_counters_lock);
+#endif
 	return NOTIFY_OK;
 }
 
 static int __init percpu_counter_startup(void)
 {
+	compute_batch_value();
 	hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
 	return 0;
 }
 module_init(percpu_counter_startup);
-#endif

--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH] percpu_counter: FBC_BATCH should be a variable

[Andrew Morton]

On Mon, 08 Dec 2008 09:05:04 +0100 Eric Dumazet <dada1@cosmosbay.com> wrote:

> Andrew Morton a __crit :
> > On Sun, 07 Dec 2008 19:30:10 +0100 Eric Dumazet <dada1@cosmosbay.com> wrote:
> > 
> >>> Do
> >>>
> >>> 	$EDITOR  $(grep -l hotcpu_notifier */*.c)
> >>>
> >>> and you'll see lots of code gets it right, and lots of code gets it wrong.
> >> I see nothing interesting, I must be blind.
> >>
> >> lib/percpu_counter.c: In function 'percpu_counter_startup':
> >> lib/percpu_counter.c:158: error: 'percpu_counter_hotcpu_callback' undeclared (first use in this function)
> >> lib/percpu_counter.c:158: error: (Each undeclared identifier is reported only once
> >> lib/percpu_counter.c:158: error: for each function it appears in.)
> >> make[1]: *** [lib/percpu_counter.o] Error 1
> > 
> > Perhaps you still had percpu_counter_hotcpu_callback inside #ifdef.
> > 
> > That a look at kernel/workqueue.c, fs/buffer.c.  No #ifdef CONFIG_HOTPLUG_CPU
> > needed at all.
> 
> We still need some #ifdef or we also must also delete them around "struct list_head list"
> in include/linux/percpu_counter.h and grow struct percpu_counter.
> 
> lib/percpu_counter.c: In function 'percpu_counter_hotcpu_callback':
> lib/percpu_counter.c:137: error: 'struct percpu_counter' has no member named 'list'
> lib/percpu_counter.c:137: warning: type defaults to 'int' in declaration of '__mptr'
> lib/percpu_counter.c:137: warning: initialization from incompatible pointer type
> ...
> 

Yes, this conditionality:

struct percpu_counter {
	spinlock_t lock;
	s64 count;
#ifdef CONFIG_HOTPLUG_CPU
	struct list_head list;	/* All percpu_counters are on a list */
#endif
	s32 *counters;
};

mucked up our nice scheme.  Oh well.

> +static void compute_batch_value(void)
> +{
> +	int nr = num_online_cpus();
> +
> +	percpu_counter_batch = max(32, nr*2);
> +}
> +
>  static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
>  					unsigned long action, void *hcpu)
>  {
> +#ifdef CONFIG_HOTPLUG_CPU
>  	unsigned int cpu;
>  	struct percpu_counter *fbc;
>  
> +	compute_batch_value();
>  	if (action != CPU_DEAD)
>  		return NOTIFY_OK;
>  
> @@ -137,13 +146,14 @@ static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
>  		spin_unlock_irqrestore(&fbc->lock, flags);
>  	}
>  	mutex_unlock(&percpu_counters_lock);
> +#endif
>  	return NOTIFY_OK;
>  }
>  
>  static int __init percpu_counter_startup(void)
>  {
> +	compute_batch_value();
>  	hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
>  	return 0;
>  }
>  module_init(percpu_counter_startup);

compute_batch_value() can be __cpuinit, but I think we're close enough
here ;)