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| author | Eric Dumazet <eric.dumazet@gmail.com> | 2011-09-19 05:52:27 +0000 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2011-09-28 13:29:50 -0400 |
| commit | 16e5726269611b71c930054ffe9b858c1cea88eb (patch) | |
| tree | 50d25ec97d639b418964bad2f45774d657468c74 /net/core/scm.c | |
| parent | a9e9fd7182332d0cf5f3e601df3e71dd431b70d7 (diff) | |
| download | linux-16e5726269611b71c930054ffe9b858c1cea88eb.tar.bz2 | |
af_unix: dont send SCM_CREDENTIALS by default
Since commit 7361c36c5224 (af_unix: Allow credentials to work across
user and pid namespaces) af_unix performance dropped a lot.
This is because we now take a reference on pid and cred in each write(),
and release them in read(), usually done from another process,
eventually from another cpu. This triggers false sharing.
# Events: 154K cycles
#
# Overhead Command Shared Object Symbol
# ........ ....... .................. .........................
#
10.40% hackbench [kernel.kallsyms] [k] put_pid
8.60% hackbench [kernel.kallsyms] [k] unix_stream_recvmsg
7.87% hackbench [kernel.kallsyms] [k] unix_stream_sendmsg
6.11% hackbench [kernel.kallsyms] [k] do_raw_spin_lock
4.95% hackbench [kernel.kallsyms] [k] unix_scm_to_skb
4.87% hackbench [kernel.kallsyms] [k] pid_nr_ns
4.34% hackbench [kernel.kallsyms] [k] cred_to_ucred
2.39% hackbench [kernel.kallsyms] [k] unix_destruct_scm
2.24% hackbench [kernel.kallsyms] [k] sub_preempt_count
1.75% hackbench [kernel.kallsyms] [k] fget_light
1.51% hackbench [kernel.kallsyms] [k]
__mutex_lock_interruptible_slowpath
1.42% hackbench [kernel.kallsyms] [k] sock_alloc_send_pskb
This patch includes SCM_CREDENTIALS information in a af_unix message/skb
only if requested by the sender, [man 7 unix for details how to include
ancillary data using sendmsg() system call]
Note: This might break buggy applications that expected SCM_CREDENTIAL
from an unaware write() system call, and receiver not using SO_PASSCRED
socket option.
If SOCK_PASSCRED is set on source or destination socket, we still
include credentials for mere write() syscalls.
Performance boost in hackbench : more than 50% gain on a 16 thread
machine (2 quad-core cpus, 2 threads per core)
hackbench 20 thread 2000
4.228 sec instead of 9.102 sec
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/core/scm.c')
| -rw-r--r-- | net/core/scm.c | 10 |
1 files changed, 6 insertions, 4 deletions
diff --git a/net/core/scm.c b/net/core/scm.c index 811b53fb330e..ff52ad0a5150 100644 --- a/net/core/scm.c +++ b/net/core/scm.c @@ -173,7 +173,7 @@ int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p) if (err) goto error; - if (pid_vnr(p->pid) != p->creds.pid) { + if (!p->pid || pid_vnr(p->pid) != p->creds.pid) { struct pid *pid; err = -ESRCH; pid = find_get_pid(p->creds.pid); @@ -183,8 +183,9 @@ int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p) p->pid = pid; } - if ((p->cred->euid != p->creds.uid) || - (p->cred->egid != p->creds.gid)) { + if (!p->cred || + (p->cred->euid != p->creds.uid) || + (p->cred->egid != p->creds.gid)) { struct cred *cred; err = -ENOMEM; cred = prepare_creds(); @@ -193,7 +194,8 @@ int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p) cred->uid = cred->euid = p->creds.uid; cred->gid = cred->egid = p->creds.gid; - put_cred(p->cred); + if (p->cred) + put_cred(p->cred); p->cred = cred; } break; |