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Message-ID: <1316406528.2521.15.camel@edumazet-laptop>
Date: Mon, 19 Sep 2011 06:28:48 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: David Miller <davem@...emloft.net>
Cc: tim.c.chen@...ux.intel.com, zheng.z.yan@...el.com,
yanzheng@...n.com, netdev@...r.kernel.org, sfr@...b.auug.org.au,
jirislaby@...il.com, sedat.dilek@...il.com, alex.shi@...el.com,
Valdis.Kletnieks@...edu
Subject: Re: [PATCH net-next] af_unix: dont send SCM_CREDENTIALS by default
Le dimanche 18 septembre 2011 à 21:07 -0400, David Miller a écrit :
> Eric, please respin your patches against current net-next, thanks!
Sure, here it is :
Its a bit different, so I didnt add Tim 'Acked-by'
[PATCH net-next] 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.
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@...il.com>
---
include/net/scm.h | 5 ++---
net/core/scm.c | 10 ++++++----
net/netlink/af_netlink.c | 5 ++---
net/unix/af_unix.c | 4 +++-
4 files changed, 13 insertions(+), 11 deletions(-)
diff --git a/include/net/scm.h b/include/net/scm.h
index 745460f..d456f4c 100644
--- a/include/net/scm.h
+++ b/include/net/scm.h
@@ -49,7 +49,7 @@ static __inline__ void scm_set_cred(struct scm_cookie *scm,
struct pid *pid, const struct cred *cred)
{
scm->pid = get_pid(pid);
- scm->cred = get_cred(cred);
+ scm->cred = cred ? get_cred(cred) : NULL;
cred_to_ucred(pid, cred, &scm->creds);
}
@@ -73,8 +73,7 @@ static __inline__ void scm_destroy(struct scm_cookie *scm)
static __inline__ int scm_send(struct socket *sock, struct msghdr *msg,
struct scm_cookie *scm)
{
- scm_set_cred(scm, task_tgid(current), current_cred());
- scm->fp = NULL;
+ memset(scm, 0, sizeof(*scm));
unix_get_peersec_dgram(sock, scm);
if (msg->msg_controllen <= 0)
return 0;
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;
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 4330db9..1201b6d 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1324,10 +1324,9 @@ static int netlink_sendmsg(struct kiocb *kiocb, struct socket *sock,
if (msg->msg_flags&MSG_OOB)
return -EOPNOTSUPP;
- if (NULL == siocb->scm) {
+ if (NULL == siocb->scm)
siocb->scm = &scm;
- memset(&scm, 0, sizeof(scm));
- }
+
err = scm_send(sock, msg, siocb->scm);
if (err < 0)
return err;
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index ec68e1c..90c55c6 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1381,8 +1381,10 @@ static int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)
static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool send_fds)
{
int err = 0;
+
UNIXCB(skb).pid = get_pid(scm->pid);
- UNIXCB(skb).cred = get_cred(scm->cred);
+ if (scm->cred)
+ UNIXCB(skb).cred = get_cred(scm->cred);
UNIXCB(skb).fp = NULL;
if (scm->fp && send_fds)
err = unix_attach_fds(scm, skb);
--
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