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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
…