Re: [PATCH v9 15/16] entry: Inline syscall_exit_work()

On 04/12/2025 09:21, Jinjie Ruan wrote:

After switch arm64 to Generic Entry, a new hotspot syscall_exit_work() appeared because syscall_exit_work() is no longer inlined. so inline

Before this series the call to syscall_trace_exit() in el0_svc_common() could not be inlined, so "no longer inlined" doesn't seem to be accurate.

syscall_exit_work(), and it has 2.6% performance uplift on perf bench basic syscall on kunpeng920 as below.

That seems strange. syscall_exit_work() is only called if some flag in SYSCALL_WORK_EXIT is set, which means that we're doing something special like tracing. That shouldn't be the case when running a simple perf bench syscall.

Also worth nothing that its counterpart (syscall_trace_enter())) is not currently inlined, the asymmetry would have to be justified.

| Metric     | W/O this patch | With this patch | Change    |
| ---------- | -------------- | --------------- | --------- |
| Total time | 2.171 [sec]    | 2.114 [sec]     |  ↓2.6%    |
| usecs/op   | 0.217192       | 0.211453        |  ↓2.6%    |
| ops/sec    | 4,604,225      | 4,729,178       |  ↑2.7%    |

Signed-off-by: Jinjie Ruan ruanjinjie@huawei.com

include/linux/entry-common.h | 63 ++++++++++++++++++++++++++++++++++- kernel/entry/syscall-common.c | 59 ++------------------------------

These changes are purely generic, surely all architectures using GENERIC_ENTRY should get similar benefits (assuming LTO isn't used)?

2 files changed, 64 insertions(+), 58 deletions(-)

diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h index cd6dacb2d8bf..2f84377fb016 100644 --- a/include/linux/entry-common.h +++ b/include/linux/entry-common.h @@ -2,6 +2,7 @@ #ifndef __LINUX_ENTRYCOMMON_H #define __LINUX_ENTRYCOMMON_H +#include <linux/audit.h> #include <linux/irq-entry-common.h> #include <linux/ptrace.h> #include <linux/seccomp.h> @@ -128,6 +129,41 @@ static __always_inline long syscall_enter_from_user_mode(struct pt_regs *regs, l return ret; } +/*

• • If SYSCALL_EMU is set, then the only reason to report is when
• • SINGLESTEP is set (i.e. PTRACE_SYSEMU_SINGLESTEP). This syscall
• • instruction has been already reported in syscall_enter_from_user_mode().
• */

+static __always_inline bool report_single_step(unsigned long work) +{

• if (work & SYSCALL_WORK_SYSCALL_EMU)

• return false;
  

• return work & SYSCALL_WORK_SYSCALL_EXIT_TRAP;

+}

+/**

• • arch_ptrace_report_syscall_exit - Architecture specific

• • 		     ptrace_report_syscall_exit.
    

• • Invoked from syscall_exit_work() to wrap ptrace_report_syscall_exit().
• • The main purpose is to support arch-specific ptrace_report_syscall_exit
• • implementation.
• */

+static __always_inline void arch_ptrace_report_syscall_exit(struct pt_regs *regs,

• 					    int step);
  

+#ifndef arch_ptrace_report_syscall_exit +static __always_inline void arch_ptrace_report_syscall_exit(struct pt_regs *regs,

• 					    int step)
  

+{

• ptrace_report_syscall_exit(regs, step);

+} +#endif

If we want syscall_exit_work() to be inline, then why would we define this hook in syscall-common.c in patch 12? Might as well define both hooks in entry-common.h right away and avoid some noise here.

- Kevin

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