Eric Dumazet a écrit :
David Miller a écrit :
From: Eric Dumazet <dada1@xxxxxxxxxxxxx>
Date: Fri, 21 Nov 2008 09:51:32 +0100
Now, I wish sockets and pipes not going through dcache, not tbench
affair
of course but real workloads...
running 8 processes on a 8 way machine doing a
for (;;)
close(socket(AF_INET, SOCK_STREAM, 0));
is slow as hell, we hit so many contended cache lines ...
ticket spin locks are slower in this case (dcache_lock for example
is taken twice when we allocate a socket(), once in d_alloc(),
another one
in d_instantiate())
As you of course know, this used to be a ton worse. At least now
these things are unhashed. :)
Well, this is dust compared to what we currently have.
To allocate a socket we :
0) Do the usual file manipulation (pretty scalable these days)
(but recent drop_file_write_access() and co slow down a bit)
1) allocate an inode with new_inode()
This function :
- locks inode_lock,
- dirties nr_inodes counter
- dirties inode_in_use list (for sockets, I doubt it is usefull)
- dirties superblock s_inodes.
- dirties last_ino counter
All these are in different cache lines of course.
2) allocate a dentry
d_alloc() takes dcache_lock,
insert dentry on its parent list (dirtying sock_mnt->mnt_sb->s_root)
dirties nr_dentry
3) d_instantiate() dentry (dcache_lock taken again)
4) init_file() -> atomic_inc on sock_mnt->refcount (in case we want to
umount this vfs ...)
At close() time, we must undo the things. Its even more expensive because
of the _atomic_dec_and_lock() that stress a lot, and because of two
cache lines that are touched when an element is deleted from a list.
for (i = 0; i < 1000*1000; i++)
close(socket(socket(AF_INET, SOCK_STREAM, 0));
Cost if run one one cpu :
real 0m1.561s
user 0m0.092s
sys 0m1.469s
If run on 8 CPUS :
real 0m27.496s
user 0m0.657s
sys 3m39.092s
[PATCH] fs: pipe/sockets/anon dentries should not have a parent
Linking pipe/sockets/anon dentries to one root 'parent' has no functional
impact at all, but a scalability one.
We can avoid touching a cache line at allocation stage (inside d_alloc(), no need
to touch root->d_count), but also at freeing time (in d_kill, decrementing d_count)
We avoid an expensive atomic_dec_and_lock() call on the root dentry.
If we correct dnotify_parent() and inotify_d_instantiate() to take into account
a NULL d_parent, we can call d_alloc() with a NULL parent instead of root dentry.
Before patch, time to run 8 millions of close(socket()) calls on 8 CPUS was :
real 0m27.496s
user 0m0.657s
sys 3m39.092s
After patch :
real 0m23.997s
user 0m0.682s
sys 3m11.193s
Old oprofile :
CPU: Core 2, speed 3000.11 MHz (estimated)
Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask of 0x00 (Unhalted core cycles) count 100000
samples cum. samples % cum. % symbol name
164257 164257 11.0245 11.0245 init_file
155488 319745 10.4359 21.4604 d_alloc
151887 471632 10.1942 31.6547 _atomic_dec_and_lock
91620 563252 6.1493 37.8039 inet_create
74245 637497 4.9831 42.7871 kmem_cache_alloc
46702 684199 3.1345 45.9216 dentry_iput
46186 730385 3.0999 49.0215 tcp_close
42824 773209 2.8742 51.8957 kmem_cache_free
37275 810484 2.5018 54.3975 wake_up_inode
36553 847037 2.4533 56.8508 tcp_v4_init_sock
35661 882698 2.3935 59.2443 inotify_d_instantiate
32998 915696 2.2147 61.4590 sysenter_past_esp
31442 947138 2.1103 63.5693 d_instantiate
31303 978441 2.1010 65.6703 generic_forget_inode
27533 1005974 1.8479 67.5183 vfs_dq_drop
24237 1030211 1.6267 69.1450 sock_attach_fd
19290 1049501 1.2947 70.4397 __copy_from_user_ll
New oprofile :
CPU: Core 2, speed 3000.24 MHz (estimated)
Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask of 0x00 (Unhalted core cycles) count 100000
samples cum. samples % cum. % symbol name
147287 147287 10.3984 10.3984 new_inode
144884 292171 10.2287 20.6271 inet_create
93670 385841 6.6131 27.2402 init_file
89852 475693 6.3435 33.5837 wake_up_inode
80910 556603 5.7122 39.2959 kmem_cache_alloc
53588 610191 3.7833 43.0792 _atomic_dec_and_lock
44341 654532 3.1305 46.2096 generic_forget_inode
38710 693242 2.7329 48.9425 kmem_cache_free
37605 730847 2.6549 51.5974 tcp_v4_init_sock
37228 768075 2.6283 54.2257 d_alloc
34085 802160 2.4064 56.6321 tcp_close
32550 834710 2.2980 58.9301 sysenter_past_esp
25931 860641 1.8307 60.7608 vfs_dq_drop
24458 885099 1.7267 62.4875 d_kill
22015 907114 1.5542 64.0418 dentry_iput
18877 925991 1.3327 65.3745 __copy_from_user_ll
17873 943864 1.2618 66.6363 mwait_idle
Signed-off-by: Eric Dumazet <dada1@xxxxxxxxxxxxx>
---
fs/anon_inodes.c | 2 +-
fs/dnotify.c | 2 +-
fs/inotify.c | 2 +-
fs/pipe.c | 2 +-
net/socket.c | 2 +-
5 files changed, 5 insertions(+), 5 deletions(-)
diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index 3662dd4..22cce87 100644
--- a/fs/anon_inodes.c
+++ b/fs/anon_inodes.c
@@ -92,7 +92,7 @@ int anon_inode_getfd(const char *name, const struct file_operations *fops,
this.name = name;
this.len = strlen(name);
this.hash = 0;
- dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this);
+ dentry = d_alloc(NULL, &this);
if (!dentry)
goto err_put_unused_fd;
diff --git a/fs/dnotify.c b/fs/dnotify.c
index 676073b..66066a3 100644
--- a/fs/dnotify.c
+++ b/fs/dnotify.c
@@ -173,7 +173,7 @@ void dnotify_parent(struct dentry *dentry, unsigned long event)
spin_lock(&dentry->d_lock);
parent = dentry->d_parent;
- if (parent->d_inode->i_dnotify_mask & event) {
+ if (parent && parent->d_inode->i_dnotify_mask & event) {
dget(parent);
spin_unlock(&dentry->d_lock);
__inode_dir_notify(parent->d_inode, event);
diff --git a/fs/inotify.c b/fs/inotify.c
index 7bbed1b..9f051bb 100644
--- a/fs/inotify.c
+++ b/fs/inotify.c
@@ -270,7 +270,7 @@ void inotify_d_instantiate(struct dentry *entry, struct inode *inode)
spin_lock(&entry->d_lock);
parent = entry->d_parent;
- if (parent->d_inode && inotify_inode_watched(parent->d_inode))
+ if (parent && parent->d_inode && inotify_inode_watched(parent->d_inode))
entry->d_flags |= DCACHE_INOTIFY_PARENT_WATCHED;
spin_unlock(&entry->d_lock);
}
diff --git a/fs/pipe.c b/fs/pipe.c
index 7aea8b8..4b961bc 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -926,7 +926,7 @@ struct file *create_write_pipe(int flags)
goto err;
err = -ENOMEM;
- dentry = d_alloc(pipe_mnt->mnt_sb->s_root, &name);
+ dentry = d_alloc(NULL, &name);
if (!dentry)
goto err_inode;
diff --git a/net/socket.c b/net/socket.c
index e9d65ea..b84de7d 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -373,7 +373,7 @@ static int sock_attach_fd(struct socket *sock, struct file *file, int flags)
struct dentry *dentry;
struct qstr name = { .name = "" };
- dentry = d_alloc(sock_mnt->mnt_sb->s_root, &name);
+ dentry = d_alloc(NULL, &name);
if (unlikely(!dentry))
return -ENOMEM;
