From: Eric Dumazet Subject: [PATCH] percpu_counter: FBC_BATCH might be too big Date: Fri, 05 Dec 2008 17:05:16 +0100 Message-ID: <4939513C.3090101@cosmosbay.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Peter Zijlstra , Mike Travis , "David S. Miller" , linux kernel , Christoph Lameter , linux-ext4@vger.kernel.org To: Andrew Morton Return-path: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org 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 --- 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