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Date: Fri, 21 Nov 2008 16:13:38 +0100
From: Eric Dumazet <dada1@...mosbay.com>
To: David Miller <davem@...emloft.net>, mingo@...e.hu
CC: cl@...ux-foundation.org, rjw@...k.pl, linux-kernel@...r.kernel.org,
kernel-testers@...r.kernel.org, efault@....de,
a.p.zijlstra@...llo.nl, Linux Netdev List <netdev@...r.kernel.org>
Subject: [PATCH] fs: pipe/sockets/anon dentries should not have a parent
Eric Dumazet a écrit :
> David Miller a écrit :
>> From: Eric Dumazet <dada1@...mosbay.com>
>> 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@...mosbay.com>
---
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(-)
View attachment "null_parent.patch" of type "text/plain" (2077 bytes)
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