Re: [PATCH v9 15/16] entry: Inline syscall_exit_work()
From: Kevin Brodsky <hidden>
Date: 2025-12-09 13:48:59
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linux-kselftest, lkml
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 <redacted>
---
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)?
quoted hunk ↗ jump to hunk
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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