From 2f970d83576cf4938fd75551c465050f6a16c33c Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 17 Jan 2006 02:54:36 -0800 Subject: [PATCH] [IPV4]: rt_cache_stat can be statically defined Using __get_cpu_var(obj) is slightly faster than per_cpu_ptr(obj, raw_smp_processor_id()). 1) Smaller code and memory use For static and small objects, DEFINE_PER_CPU(type, object) is preferred over a alloc_percpu() : Better and smaller code to access them, and no extra memory (storing the pointer, and the percpu array of pointers) x86_64 code before patch mov 1237577(%rip),%rax # ffffffff803e5990 not %rax # part of per_cpu machinery mov %gs:0x3c,%edx # get cpu number movslq %edx,%rdx # extend 32 bits cpu number to 64 bits mov (%rax,%rdx,8),%rax # get the pointer for this cpu incl 0x38(%rax) x86_64 code after patch mov $per_cpu__rt_cache_stat,%rdx mov %gs:0x48,%rax # get percpu data offset incl 0x38(%rax,%rdx,1) 2) False sharing avoidance for SMP : For a small NR_CPUS, the array of per cpu pointers allocated in alloc_percpu() can be <= 32 bytes. This let slab code gives a part of a cache line. If the other part of this 64 bytes (or 128 bytes) cache line is used by a mostly written object, we can have false sharing and expensive per_cpu_ptr() operations. Size of rt_cache_stat is 64 bytes, so this patch is not a danger of a too big increase of bss (in UP mode) or static per_cpu data for SMP (PERCPU_ENOUGH_ROOM is currently 32768 bytes) Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/route.c | 14 ++++---------- 1 file changed, 4 insertions(+), 10 deletions(-) diff --git a/net/ipv4/route.c b/net/ipv4/route.c index f701a136a6ae..f2e82afc15b3 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -240,9 +240,8 @@ static unsigned rt_hash_mask; static int rt_hash_log; static unsigned int rt_hash_rnd; -static struct rt_cache_stat *rt_cache_stat; -#define RT_CACHE_STAT_INC(field) \ - (per_cpu_ptr(rt_cache_stat, raw_smp_processor_id())->field++) +static DEFINE_PER_CPU(struct rt_cache_stat, rt_cache_stat); +#define RT_CACHE_STAT_INC(field) (__get_cpu_var(rt_cache_stat).field++) static int rt_intern_hash(unsigned hash, struct rtable *rth, struct rtable **res); @@ -401,7 +400,7 @@ static void *rt_cpu_seq_start(struct seq_file *seq, loff_t *pos) if (!cpu_possible(cpu)) continue; *pos = cpu+1; - return per_cpu_ptr(rt_cache_stat, cpu); + return &per_cpu(rt_cache_stat, cpu); } return NULL; } @@ -414,7 +413,7 @@ static void *rt_cpu_seq_next(struct seq_file *seq, void *v, loff_t *pos) if (!cpu_possible(cpu)) continue; *pos = cpu+1; - return per_cpu_ptr(rt_cache_stat, cpu); + return &per_cpu(rt_cache_stat, cpu); } return NULL; @@ -3160,10 +3159,6 @@ int __init ip_rt_init(void) ipv4_dst_ops.gc_thresh = (rt_hash_mask + 1); ip_rt_max_size = (rt_hash_mask + 1) * 16; - rt_cache_stat = alloc_percpu(struct rt_cache_stat); - if (!rt_cache_stat) - return -ENOMEM; - devinet_init(); ip_fib_init(); @@ -3191,7 +3186,6 @@ int __init ip_rt_init(void) if (!proc_net_fops_create("rt_cache", S_IRUGO, &rt_cache_seq_fops) || !(rtstat_pde = create_proc_entry("rt_cache", S_IRUGO, proc_net_stat))) { - free_percpu(rt_cache_stat); return -ENOMEM; } rtstat_pde->proc_fops = &rt_cpu_seq_fops; -- 2.30.2