Re: [PATCH v4 0/8] Generic IRQ entry/exit support for powerpc

Samir M
2026-01-30T18:15:09Z

On 23/01/26 1:09 pm, Mukesh Kumar Chaurasiya wrote:
> Adding support for the generic irq entry/exit handling for PowerPC. The
> goal is to bring PowerPC in line with other architectures that already
> use the common irq entry infrastructure, reducing duplicated code and
> making it easier to share future changes in entry/exit paths.
>
> This is slightly tested of ppc64le and ppc32.
>
> The performance benchmarks are below:
>
> perf bench syscall usec/op (-ve is improvement)
>
> | Syscall | Base | test | change % |
> | ------- | ----------- | ----------- | -------- |
> | basic | 0.093543 | 0.093023 | -0.56 |
> | execve | 446.557781 | 450.107172 | +0.79 |
> | fork | 1142.204391 | 1156.377214 | +1.24 |
> | getpgid | 0.097666 | 0.092677 | -5.11 |
>
> perf bench syscall ops/sec (+ve is improvement)
>
> | Syscall | Base | New | change % |
> | ------- | -------- | -------- | -------- |
> | basic | 10690548 | 10750140 | +0.56 |
> | execve | 2239 | 2221 | -0.80 |
> | fork | 875 | 864 | -1.26 |
> | getpgid | 10239026 | 10790324 | +5.38 |
>
>
> IPI latency benchmark (-ve is improvement)
>
> | Metric | Base (ns) | New (ns) | % Change |
> | -------------- | ------------- | ------------- | -------- |
> | Dry run | 583136.56 | 584136.35 | 0.17% |
> | Self IPI | 4167393.42 | 4149093.90 | -0.44% |
> | Normal IPI | 61769347.82 | 61753728.39 | -0.03% |
> | Broadcast IPI | 2235584825.02 | 2227521401.45 | -0.36% |
> | Broadcast lock | 2164964433.31 | 2125658641.76 | -1.82% |
>
>
> Thats very close to performance earlier with arch specific handling.
>
> Tests done:
> - Build and boot on ppc64le pseries.
> - Build and boot on ppc64le powernv8 powernv9 powernv10.
> - Build and boot on ppc32.
> - Performance benchmark done with perf syscall basic on pseries.
>
> Changelog:
> V3 -> V4
> - Fixed the issue in older gcc version where linker couldn't find
> mem functions
> - Merged IRQ enable and syscall enable into a single patch
> - Cleanup for unused functions done in separate patch.
> - Some other cosmetic changes
> V3: https://lore.kernel.org/all/20251229045416.3193779-1-mkchauras@linux.ibm.com/
>
> V2 -> V3
> - #ifdef CONFIG_GENERIC_IRQ_ENTRY removed from unnecessary places
> - Some functions made __always_inline
> - pt_regs padding changed to match 16byte interrupt stack alignment
> - And some cosmetic changes from reviews from earlier patch
> V2: https://lore.kernel.org/all/20251214130245.43664-1-mkchauras@linux.ibm.com/
>
> V1 -> V2
> - Fix an issue where context tracking was showing warnings for
> incorrect context
> V1: https://lore.kernel.org/all/20251102115358.1744304-1-mkchauras@linux.ibm.com/
>
> RFC -> PATCH V1
> - Fix for ppc32 spitting out kuap lock warnings.
> - ppc64le powernv8 crash fix.
> - Review comments incorporated from previous RFC.
> RFC https://lore.kernel.org/all/20250908210235.137300-2-mchauras@linux.ibm.com/
>
> Mukesh Kumar Chaurasiya (8):
> powerpc: rename arch_irq_disabled_regs
> powerpc: Prepare to build with generic entry/exit framework
> powerpc: introduce arch_enter_from_user_mode
> powerpc: Introduce syscall exit arch functions
> powerpc: add exit_flags field in pt_regs
> powerpc: Prepare for IRQ entry exit
> powerpc: Enable GENERIC_ENTRY feature
> powerpc: Remove unused functions
>
> arch/powerpc/Kconfig | 1 +
> arch/powerpc/include/asm/entry-common.h | 533 ++++++++++++++++++++++++
> arch/powerpc/include/asm/hw_irq.h | 4 +-
> arch/powerpc/include/asm/interrupt.h | 386 +++--------------
> arch/powerpc/include/asm/kasan.h | 15 +-
> arch/powerpc/include/asm/ptrace.h | 6 +-
> arch/powerpc/include/asm/signal.h | 1 -
> arch/powerpc/include/asm/stacktrace.h | 6 +
> arch/powerpc/include/asm/syscall.h | 5 +
> arch/powerpc/include/asm/thread_info.h | 1 +
> arch/powerpc/include/uapi/asm/ptrace.h | 14 +-
> arch/powerpc/kernel/interrupt.c | 254 ++---------
> arch/powerpc/kernel/ptrace/ptrace.c | 142 +------
> arch/powerpc/kernel/signal.c | 25 +-
> arch/powerpc/kernel/syscall.c | 119 +-----
> arch/powerpc/kernel/traps.c | 2 +-
> arch/powerpc/kernel/watchdog.c | 2 +-
> arch/powerpc/perf/core-book3s.c | 2 +-
> 18 files changed, 690 insertions(+), 828 deletions(-)
> create mode 100644 arch/powerpc/include/asm/entry-common.h
Hi Mukesh,

I verified this patch with the following configuration and test coverage.

Test configuration:

* Kernel version: 6.19.0-rc6
* Number of CPUs: 80

Tests that are performed:
1. Kernel selftests
2. LTP
3. will-it-scale
4. stress-ng (IRQ and syscall focused)
5. DLPAR with SMT stress testing
6. DLPAR with CPU folding scenarios
7. ptrace, ftrace and perf related tests.
8. Build and boot.

No functional issues were observed during testing.

Performance Tests:
perf bench syscall usec/op:(+ve is regression)
syscall  | without_patch | with_patch |  %change |
--------------------------------------------------
getppid  |   0.100       |  0.102    |  +2.0 %  |
fork.    |   363.281     |  369.995  |  +1.85%  |
execve.  |   360.610     |  360.826  |  +0.06%  |

perf bench syscall ops/sec:(-ve is regression)
syscall  | without_patch | with_patch  |  %change |
--------------------------------------------------
getppid  |   10,048,674  | 9,851,574|   −1.96% |
fork.    |   2,752       |    2,703   |   −1.78% |
execve.  |   2,772       | 2,771    |   −0.04% |

IPI latency benchmark (-ve is improvement)

| Metric  | without_patch (ns)| with_patch (ns) | % Change |
| -------------- | ----------------- | --------------- | -------- |
| Dry run        | 202259.20        | 201962.38       | -0.15%   |
| Self IPI       | 3565899.21       | 3271122.04      | -8.27%   |
| Normal IPI     | 47146345.28       | 42920014.89     | -8.97%   |
| Broadcast IPI  | 3920749623.87     | 3838799420.04   | -2.09%   |
| Broadcast lock | 3877260906.55     | 3803805814.03   | -1.89%   |

Please add the below tag,

Tested-by: Samir M <samir@linux.ibm.com>

Regards,
Samir.