Eric Dumazet 16e5726269 af_unix: dont send SCM_CREDENTIALS by default ... Since commit 7361c36c52 (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>		2011-09-28 13:29:50 -04:00
..
acpi	Merge branch 'apei-release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux-acpi-2.6	2011-08-03 21:53:27 -10:00
asm-generic	All Arch: remove linkage for sys_nfsservctl system call	2011-08-26 15:09:58 -07:00
crypto
drm	drm: Separate EDID Header Check from EDID Block Check	2011-08-04 14:39:35 +01:00
keys
linux	net: introduce ptp one step time stamp mode for sync packets	2011-09-26 16:02:46 -04:00
math-emu
media	[media] V4L: initial driver for ov5642 CMOS sensor	2011-07-27 17:56:09 -03:00
mtd
net	af_unix: dont send SCM_CREDENTIALS by default	2011-09-28 13:29:50 -04:00
pcmcia	pcmcia: add PCMCIA_DEVICE_MANF_CARD_PROD_ID3	2011-08-08 16:04:11 -04:00
rdma	net: consolidate and fix ethtool_ops->get_settings calling	2011-09-15 17:32:26 -04:00
rxrpc	atomic: use <linux/atomic.h>	2011-07-26 16:49:47 -07:00
scsi	Merge branch 'for-linus' of git://git.open-osd.org/linux-open-osd	2011-08-06 22:56:03 -07:00
sound	ASoC: omap: Update e-mail address of Jarkko Nikula	2011-08-12 11:45:10 +09:00
target	target: Make standard INQUIRY return 'not connected' for tpg_virt_lun0	2011-08-22 19:25:35 +00:00
trace	Merge branch 'for-linus' of git://git.kernel.dk/linux-block	2011-08-19 10:47:07 -07:00
video	OMAP: DSS2: Remove unused opt_clock_available	2011-07-25 10:22:05 +03:00
xen	xen/balloon: memory hotplug support for Xen balloon driver	2011-07-25 20:57:08 -07:00
Kbuild