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Zhen Lei 4030ddfd0e arm64: entry: Improve the performance of system calls 
Commit 582f95835a ("arm64: entry: convert el0_sync to C") converted lots
of functions from assembly to C, this greatly improves readability. But
el0_svc()/el0_svc_compat() is in response to system call requests from
user mode and may be in the hot path.

Although the SVC is in the first case of the switch statement in C, the
compiler optimizes the switch statement as a whole, and does not give SVC
a small boost.

Use "likely()" to help SVC directly invoke its handler after a simple
judgment to avoid entering the switch table lookup process.

After:
0000000000000ff0 <el0t_64_sync_handler>:
     ff0:       d503245f        bti     c
     ff4:       d503233f        paciasp
     ff8:       a9bf7bfd        stp     x29, x30, [sp, #-16]!
     ffc:       910003fd        mov     x29, sp
    1000:       d5385201        mrs     x1, esr_el1
    1004:       531a7c22        lsr     w2, w1, #26
    1008:       f100545f        cmp     x2, #0x15
    100c:       540000a1        b.ne    1020 <el0t_64_sync_handler+0x30>
    1010:       97fffe14        bl      860 <el0_svc>
    1014:       a8c17bfd        ldp     x29, x30, [sp], #16
    1018:       d50323bf        autiasp
    101c:       d65f03c0        ret
    1020:       f100705f        cmp     x2, #0x1c

Execute "./lat_syscall null" on my board (BogoMIPS : 200.00), it can save
about 10ns.

Before:
Simple syscall: 0.2365 microseconds
Simple syscall: 0.2354 microseconds
Simple syscall: 0.2339 microseconds

After:
Simple syscall: 0.2255 microseconds
Simple syscall: 0.2254 microseconds
Simple syscall: 0.2256 microseconds

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
 		2023-05-09 15:50:47 +02:00
Documentation Rust fixes for v6.3 2023-04-20 12:46:18 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
arch arm64: entry: Improve the performance of system calls 2023-05-09 15:50:47 +02:00
block Revert "block: Merge bio before checking ->cached_rq" 2023-04-20 06:54:17 -06:00
certs Kbuild updates for v6.3 2023-02-26 11:53:25 -08:00
crypto asymmetric_keys: log on fatal failures in PE/pkcs7 2023-03-21 16:23:56 +00:00
drivers bus: fsl-mc-bus: fix dma error message for dpio devices 2023-05-09 15:50:46 +02:00
fs btrfs: fix uninitialized variable warnings 2023-05-01 08:32:26 +09:00
include drivers/mmc/host/sdhci-of-esdhc : Fix DMA coherent check in ACPI mode. 2023-05-09 15:48:24 +02:00
init gcc: disable '-Warray-bounds' for gcc-13 too 2023-04-23 09:56:20 -07:00
io_uring io_uring-6.3-2023-04-14 2023-04-15 10:29:53 -07:00
ipc Merge branch 'work.namespace' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2023-02-24 19:20:07 -08:00
kernel Networking fixes for 6.3-rc8, including fixes from netfilter and bpf 2023-04-20 11:03:51 -07:00
lib maple_tree: fix mas_empty_area() search 2023-04-18 14:22:13 -07:00
mm mm/mremap: fix vm_pgoff in vma_merge() case 3 2023-05-01 08:32:26 +09:00
net bluetooth: Perform careful capability checks in hci_sock_ioctl() 2023-05-01 08:32:25 +09:00
rust rust: allow to use INIT_STACK_ALL_ZERO 2023-04-19 19:34:43 +02:00
samples LoongArch changes for v6.3 2023-03-01 09:27:00 -08:00
scripts Kbuild fixes for v6.3 (4th) 2023-04-23 08:22:25 -07:00
security keys: Do not cache key in task struct if key is requested from kernel thread 2023-03-21 16:22:40 +00:00
sound ALSA: hda/realtek: fix mute/micmute LEDs for a HP ProBook 2023-04-20 07:13:12 +02:00
tools 22 hotfixes. 2023-04-19 17:55:45 -07:00
usr initramfs: Check negative timestamp to prevent broken cpio archive 2023-04-16 17:37:01 +09:00
virt KVM: PPC: Make KVM_CAP_IRQFD_RESAMPLE platform dependent 2023-03-31 11:19:05 -04:00
.clang-format cpumask: re-introduce constant-sized cpumask optimizations 2023-03-05 14:30:34 -08:00
.cocciconfig
…
.get_maintainer.ignore
…
.gitattributes .gitattributes: use 'dts' diff driver for *.dtso files 2023-02-26 15:28:23 +09:00
.gitignore kbuild: rpm-pkg: move source components to rpmbuild/SOURCES 2023-03-16 22:45:56 +09:00
.mailmap Networking fixes for 6.3-rc8, including fixes from netfilter and bpf 2023-04-20 11:03:51 -07:00
.rustfmt.toml
…
COPYING
…
CREDITS There is no particular theme here - mainly quick hits all over the tree. 2023-02-23 17:55:40 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig
…
MAINTAINERS MAINTAINERS: Resume MPTCP co-maintainer role 2023-04-19 18:10:24 -07:00
Makefile Linux 6.3.1 2023-05-01 08:32:26 +09:00
README
…

README 

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

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

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.