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c6f4a90022
The arch_spin_value_unlocked() of ticket-lock would cause the compiler to
generate inefficient asm code in riscv architecture because of
unnecessary memory access to the contended value.
Before the patch:
void lockref_get(struct lockref *lockref)
{
78: fd010113 add sp,sp,-48
7c: 02813023 sd s0,32(sp)
80: 02113423 sd ra,40(sp)
84: 03010413 add s0,sp,48
0000000000000088 <.LBB296>:
CMPXCHG_LOOP(
88: 00053783 ld a5,0(a0)
After the patch:
void lockref_get(struct lockref *lockref)
{
CMPXCHG_LOOP(
78: 00053783 ld a5,0(a0)
After the patch, the lockref_get() could get in a fast path instead of the
function's prologue. This is because ticket lock complex logic would
limit compiler optimization for the spinlock fast path, and qspinlock
won't.
The caller of arch_spin_value_unlocked() could benefit from this
change. Currently, the only caller is lockref.
Signed-off-by: Guo Ren <guoren@kernel.org>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20230908154339.3250567-1-guoren@kernel.org
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
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| MAINTAINERS | ||
| Makefile | ||
| 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.