percpu_counter library generates quite nasty code, so unless you need
to dynamically allocate counters or take fast approximate value, a
simple per cpu set of counters is much better.
The percpu_counter can never be made to work as well, because it has an
indirection from pointer to percpu memory, and it can't use direct
this_cpu_inc interfaces because it doesn't use static PER_CPU data, so
code will always be worse.
In the fastpath, it is the difference between this:
incl %gs:nr_dentry # nr_dentry
and this:
movl percpu_counter_batch(%rip), %edx # percpu_counter_batch,
movl $1, %esi #,
movq $nr_dentry, %rdi #,
call __percpu_counter_add # (plus I clobber registers)
__percpu_counter_add:
pushq %rbp #
movq %rsp, %rbp #,
subq $32, %rsp #,
movq %rbx, -24(%rbp) #,
movq %r12, -16(%rbp) #,
movq %r13, -8(%rbp) #,
movq %rdi, %rbx # fbc, fbc
#APP
# 216 "/home/npiggin/usr/src/linux-2.6/arch/x86/include/asm/thread_info.h" 1
movq %gs:kernel_stack,%rax #, pfo_ret__
# 0 "" 2
#NO_APP
incl -8124(%rax) # <variable>.preempt_count
movq 32(%rdi), %r12 # <variable>.counters, tcp_ptr__
#APP
# 78 "lib/percpu_counter.c" 1
add %gs:this_cpu_off, %r12 # this_cpu_off, tcp_ptr__
# 0 "" 2
#NO_APP
movslq (%r12),%r13 #* tcp_ptr__, tmp73
movslq %edx,%rax # batch, batch
addq %rsi, %r13 # amount, count
cmpq %rax, %r13 # batch, count
jge .L27 #,
negl %edx # tmp76
movslq %edx,%rdx # tmp76, tmp77
cmpq %rdx, %r13 # tmp77, count
jg .L28 #,
.L27:
movq %rbx, %rdi # fbc,
call _raw_spin_lock #
addq %r13, 8(%rbx) # count, <variable>.count
movq %rbx, %rdi # fbc,
movl $0, (%r12) #,* tcp_ptr__
call _raw_spin_unlock #
.L29:
#APP
# 216 "/home/npiggin/usr/src/linux-2.6/arch/x86/include/asm/thread_info.h" 1
movq %gs:kernel_stack,%rax #, pfo_ret__
# 0 "" 2
#NO_APP
decl -8124(%rax) # <variable>.preempt_count
movq -8136(%rax), %rax #, D.14625
testb $8, %al #, D.14625
jne .L32 #,
.L31:
movq -24(%rbp), %rbx #,
movq -16(%rbp), %r12 #,
movq -8(%rbp), %r13 #,
leave
ret
.p2align 4,,10
.p2align 3
.L28:
movl %r13d, (%r12) # count,*
jmp .L29 #
.L32:
call preempt_schedule #
.p2align 4,,6
jmp .L31 #
.size __percpu_counter_add, .-__percpu_counter_add
.p2align 4,,15
Signed-off-by: Nick Piggin <npiggin@xxxxxxxxx>
---
fs/dcache.c | 43 +++++++++++++++++++++++++++++--------------
fs/inode.c | 46 ++++++++++++++++++++++++++--------------------
2 files changed, 55 insertions(+), 34 deletions(-)
Index: linux-2.6/fs/dcache.c
===================================================================
--- linux-2.6.orig/fs/dcache.c 2010-12-10 15:39:56.000000000 +1100
+++ linux-2.6/fs/dcache.c 2010-12-10 15:42:38.000000000 +1100
@@ -67,13 +67,22 @@ struct dentry_stat_t dentry_stat = {
.age_limit = 45,
};
-static struct percpu_counter nr_dentry __cacheline_aligned_in_smp;
+static DEFINE_PER_CPU(unsigned int, nr_dentry);
#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
+static int get_nr_dentry(void)
+{
+ int i;
+ int sum = 0;
+ for_each_possible_cpu(i)
+ sum += per_cpu(nr_dentry, i);
+ return sum < 0 ? 0 : sum;
+}
+
int proc_nr_dentry(ctl_table *table, int write, void __user *buffer,
size_t *lenp, loff_t *ppos)
{
- dentry_stat.nr_dentry = percpu_counter_sum_positive(&nr_dentry);
+ dentry_stat.nr_dentry = get_nr_dentry();
return proc_dointvec(table, write, buffer, lenp, ppos);
}
#endif
@@ -93,7 +102,7 @@ static void __d_free(struct rcu_head *he
*/
static void d_free(struct dentry *dentry)
{
- percpu_counter_dec(&nr_dentry);
+ this_cpu_dec(nr_dentry);
if (dentry->d_op && dentry->d_op->d_release)
dentry->d_op->d_release(dentry);
@@ -981,7 +990,7 @@ struct dentry *d_alloc(struct dentry * p
list_add(&dentry->d_u.d_child, &parent->d_subdirs);
spin_unlock(&dcache_lock);
- percpu_counter_inc(&nr_dentry);
+ this_cpu_inc(nr_dentry);
return dentry;
}
@@ -2422,8 +2431,6 @@ static void __init dcache_init(void)
{
int loop;
- percpu_counter_init(&nr_dentry, 0);
-
/*
* A constructor could be added for stable state like the lists,
* but it is probably not worth it because of the cache nature
Index: linux-2.6/fs/inode.c
===================================================================
--- linux-2.6.orig/fs/inode.c 2010-12-10 15:39:56.000000000 +1100
+++ linux-2.6/fs/inode.c 2010-12-10 15:43:59.000000000 +1100
@@ -102,13 +102,17 @@ static DECLARE_RWSEM(iprune_sem);
*/
struct inodes_stat_t inodes_stat;
-static struct percpu_counter nr_inodes __cacheline_aligned_in_smp;
+static DEFINE_PER_CPU(unsigned int, nr_inodes);
static struct kmem_cache *inode_cachep __read_mostly;
-static inline int get_nr_inodes(void)
+static int get_nr_inodes(void)
{
- return percpu_counter_sum_positive(&nr_inodes);
+ int i;
+ int sum = 0;
+ for_each_possible_cpu(i)
+ sum += per_cpu(nr_inodes, i);
+ return sum < 0 ? 0 : sum;
}
static inline int get_nr_inodes_unused(void)
@@ -118,9 +122,9 @@ static inline int get_nr_inodes_unused(v
int get_nr_dirty_inodes(void)
{
+ /* not actually dirty inodes, but a wild approximation */
int nr_dirty = get_nr_inodes() - get_nr_inodes_unused();
return nr_dirty > 0 ? nr_dirty : 0;
-
}
/*
@@ -222,7 +226,7 @@ int inode_init_always(struct super_block
inode->i_fsnotify_mask = 0;
#endif
- percpu_counter_inc(&nr_inodes);
+ this_cpu_inc(nr_inodes);
return 0;
out:
@@ -264,7 +268,7 @@ void __destroy_inode(struct inode *inode
if (inode->i_default_acl && inode->i_default_acl != ACL_NOT_CACHED)
posix_acl_release(inode->i_default_acl);
#endif
- percpu_counter_dec(&nr_inodes);
+ this_cpu_dec(nr_inodes);
}
EXPORT_SYMBOL(__destroy_inode);
@@ -1646,7 +1650,6 @@ void __init inode_init(void)
SLAB_MEM_SPREAD),
init_once);
register_shrinker(&icache_shrinker);
- percpu_counter_init(&nr_inodes, 0);
/* Hash may have been set up in inode_init_early */
if (!hashdist)
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
