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Mel Gorman e832bf48c8 audit: Reduce overhead using a coarse clock Commit `2115bb250f` ("audit: Use timespec64 to represent audit timestamps") noted that audit timestamps were not y2038 safe and used a 64-bit timestamp. In itself, this makes sense but the conversion was from CURRENT_TIME to ktime_get_real_ts64() which is a heavier call to record an accurate timestamp which is required in some, but not all, cases. The impact is that when auditd is running without any rules that all syscalls have higher overhead. This is visible in the sysbench-thread benchmark as a 11.5% performance hit. That benchmark is dumb as rocks but it's also visible in redis as an 8-10% hit on all operations which is of greater concern. It is somewhat stupid of audit to track syscalls without any rules related to syscalls but that is how it behaves. The overhead can be directly measured with perf comparing 4.9 with 4.12 4.9 7.76% sysbench [kernel.vmlinux] [k] __schedule 7.62% sysbench [kernel.vmlinux] [k] _raw_spin_lock 7.37% sysbench libpthread-2.22.so [.] __lll_lock_elision 7.29% sysbench [kernel.vmlinux] [.] syscall_return_via_sysret 6.59% sysbench [kernel.vmlinux] [k] native_sched_clock 5.21% sysbench libc-2.22.so [.] __sched_yield 4.38% sysbench [kernel.vmlinux] [k] entry_SYSCALL_64 4.28% sysbench [kernel.vmlinux] [k] do_syscall_64 3.49% sysbench libpthread-2.22.so [.] __lll_unlock_elision 3.13% sysbench [kernel.vmlinux] [k] __audit_syscall_exit 2.87% sysbench [kernel.vmlinux] [k] update_curr 2.73% sysbench [kernel.vmlinux] [k] pick_next_task_fair 2.31% sysbench [kernel.vmlinux] [k] syscall_trace_enter 2.20% sysbench [kernel.vmlinux] [k] __audit_syscall_entry ..... 0.00% swapper [kernel.vmlinux] [k] read_tsc 4.12 7.84% sysbench [kernel.vmlinux] [k] __schedule 7.05% sysbench [kernel.vmlinux] [k] _raw_spin_lock 6.57% sysbench libpthread-2.22.so [.] __lll_lock_elision 6.50% sysbench [kernel.vmlinux] [.] syscall_return_via_sysret 5.95% sysbench [kernel.vmlinux] [k] read_tsc 5.71% sysbench [kernel.vmlinux] [k] native_sched_clock 4.78% sysbench libc-2.22.so [.] __sched_yield 4.30% sysbench [kernel.vmlinux] [k] entry_SYSCALL_64 3.94% sysbench [kernel.vmlinux] [k] do_syscall_64 3.37% sysbench libpthread-2.22.so [.] __lll_unlock_elision 3.32% sysbench [kernel.vmlinux] [k] __audit_syscall_exit 2.91% sysbench [kernel.vmlinux] [k] __getnstimeofday64 Note the additional overhead from read_tsc which goes from 0% to 5.95%. This is on a single-socket E3-1230 but similar overheads have been measured on an older machine which the patch also eliminates. The patch in question has no explanation as to why a fully-accurate timestamp is required and is likely an oversight. Using a coarser, but monotically increasing, timestamp the overhead can be eliminated. While it can be worked around by configuring or disabling audit, it's tricky enough to detect that a kernel fix is justified. With this patch, we see the following; sysbenchthread 4.9.0 4.12.0 4.12.0 vanilla vanilla coarse-v1r1 Amean 1 1.49 ( 0.00%) 1.66 ( -11.42%) 1.51 ( -1.34%) Amean 3 1.48 ( 0.00%) 1.65 ( -11.45%) 1.50 ( -0.96%) Amean 5 1.49 ( 0.00%) 1.67 ( -12.31%) 1.51 ( -1.83%) Amean 7 1.49 ( 0.00%) 1.66 ( -11.72%) 1.50 ( -0.67%) Amean 12 1.48 ( 0.00%) 1.65 ( -11.57%) 1.52 ( -2.89%) Amean 16 1.49 ( 0.00%) 1.65 ( -11.13%) 1.51 ( -1.73%) The benchmark is reporting the time required for different thread counts to lock/unlock a private mutex which, while dense, demonstrates the syscall overhead. This is showing that 4.12 took a 11-12% hit but the overhead is almost eliminated by the patch. While the variance is not reported here, it's well within the noise with the patch applied. Signed-off-by: Mel Gorman <mgorman@techsingularity.net> Acked-by: Arnd Bergmann <arnd@arndb.de> Acked-by: Deepa Dinamani <deepa.kernel@gmail.com> Signed-off-by: Paul Moore <paul@paul-moore.com>		2017-09-05 09:46:54 -04:00
arch	Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus	2017-09-03 09:50:26 -07:00
block	blk-mq-debugfs: Add names for recently added flags	2017-08-25 08:07:44 -06:00
certs	modsign: add markers to endif-statements in certs/Makefile	2017-07-14 11:01:37 +10:00
crypto	crypto: algif_skcipher - only call put_page on referenced and used pages	2017-08-22 14:45:48 +08:00
Documentation	ARM: SoC fixes for 4.13	2017-09-01 17:16:40 -07:00
drivers	Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus	2017-09-03 09:50:26 -07:00
firmware	firmware/Makefile: force recompilation if makefile changes	2017-05-08 17:15:10 -07:00
fs	Merge branch 'for-next' of git://git.samba.org/sfrench/cifs-2.6	2017-09-01 20:57:27 -07:00
include	Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip	2017-09-03 09:23:23 -07:00
init	random: do not ignore early device randomness	2017-07-12 16:26:00 -07:00
ipc	ipc: add missing container_of()s for randstruct	2017-08-02 17:16:12 -07:00
kernel	audit: Reduce overhead using a coarse clock	2017-09-05 09:46:54 -04:00
lib	Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6	2017-09-01 10:30:03 -07:00
mm	Merge branch 'akpm' (patches from Andrew)	2017-08-31 17:56:56 -07:00
net	Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net	2017-09-01 12:49:03 -07:00
samples	samples/bpf: fix bpf tunnel cleanup	2017-07-31 22:02:47 -07:00
scripts	scripts/dtc: fix '%zx' warning	2017-08-31 16:33:15 -07:00
security	Now that IPC and other changes have landed, enable manual markings for	2017-07-19 08:55:18 -07:00
sound	ASoC: Fixes for v4.13	2017-08-31 14:08:26 +02:00
tools	NTB bug fixes to address an incorrect ntb_mw_count reference in the NTB	2017-08-27 17:01:54 -07:00
usr	ramfs: clarify help text that compression applies to ramfs as well as legacy ramdisk.	2017-07-06 16:24:30 -07:00
virt	KVM: update to new mmu_notifier semantic v2	2017-08-31 16:13:00 -07:00
.cocciconfig	scripts: add Linux .cocciconfig for coccinelle	2016-07-22 12:13:39 +02:00
.get_maintainer.ignore	Add hch to .get_maintainer.ignore	2015-08-21 14:30:10 -07:00
.gitattributes	.gitattributes: set git diff driver for C source code files	2016-10-07 18:46:30 -07:00
.gitignore	kbuild: Add support to generate LLVM assembly files	2017-04-25 08:13:52 +09:00
.mailmap	power supply and reset changes for the v4.12 series (part 2)	2017-05-12 12:02:21 -07:00
COPYING
CREDITS	avr32: remove support for AVR32 architecture	2017-05-01 09:27:15 +02:00
Kbuild	kbuild: Consolidate header generation from ASM offset information	2017-04-13 05:43:37 +09:00
Kconfig
MAINTAINERS	Merge branch 'irq-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip	2017-08-20 09:07:56 -07:00
Makefile	Linux 4.13	2017-09-03 13:56:17 -07:00
README	README: add a new README file, pointing to the Documentation/	2016-10-24 08:12:35 -02:00

README

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.