From 16e5726269611b71c930054ffe9b858c1cea88eb Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 19 Sep 2011 05:52:27 +0000 Subject: 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 Acked-by: Tim Chen Signed-off-by: David S. Miller --- net/core/scm.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) (limited to 'net/core/scm.c') diff --git a/net/core/scm.c b/net/core/scm.c index 811b53f..ff52ad0 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; -- cgit v1.1