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

[Samir Alamshaha Mulani]

On 02/11/25 5:23 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 from perf bench basic syscall are below:
>
> | Metric     | W/O Generic Framework | With Generic Framework | Change |
> | ---------- | --------------------- | ---------------------- | ------ |
> | Total time | 0.939 [sec]           | 0.938 [sec]            | ~0%    |
> | usecs/op   | 0.093900              | 0.093882               | ~0%    |
> | ops/sec    | 1,06,49,615           | 1,06,51,725            | ~0%    |
>
> 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:
>
> RFC -> PATCH
>   - Fix for ppc32 spitting out kuap lock warnings.
>   - ppc64le powernv8 crash fix.
>   - Review comments incorporated from previous RFC.
> RFChttps://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 IRQ generic entry/exit path.
>    powerpc: Enable Generic Entry/Exit for syscalls.
>
>   arch/powerpc/Kconfig                    |   2 +
>   arch/powerpc/include/asm/entry-common.h | 539 ++++++++++++++++++++++++
>   arch/powerpc/include/asm/hw_irq.h       |   4 +-
>   arch/powerpc/include/asm/interrupt.h    | 401 +++---------------
>   arch/powerpc/include/asm/ptrace.h       |   3 +
>   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/asm-offsets.c       |   1 +
>   arch/powerpc/kernel/interrupt.c         | 258 +++---------
>   arch/powerpc/kernel/ptrace/ptrace.c     | 142 +------
>   arch/powerpc/kernel/signal.c            |   8 +
>   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 +-
>   17 files changed, 693 insertions(+), 816 deletions(-)
>   create mode 100644 arch/powerpc/include/asm/entry-common.h
>
Hi,

I have reviewed and tested the generic IRQ entry/exist patch series. 
Below are my observations:



Test Coverage


• Successfully ran LTP (specially syscall) and entire LTP test suite, 
without observing any regressions or issues related to the implementation.



System Configuration


• CPUs: 160


• Kernel: v6.18.0-rc1+


• Processor mode: Shared (uncapped)



Performance Evaluation


• Conducted benchmarking using perf bench syscall basic -l and hackbench.


• No functional regressions observed, and results were consistent with 
expectations.


  * Results for perf bench syscall**Loops = 100,000**

**Loops = 100,000**
| Metric       | W/O Generic Framework      | With Generic Framework    
| Improvement |
|----------|-----------------------:|-----------------------:|------------:|
| usecs/op   |              0.125328              | 0.128839            
   |     ~-2.80% |
| ops/sec     |             7,979,645              |  7,762,047          
     |     ~-2.73% |

**Loops = 1,000,000**
| Metric        | W/O Generic Framework         | With Generic 
Framework             | Improvement |
|----------|-----------------------:|-----------------------:|------------:|
| usecs/op   |              0.125015              | 0.127885            
   |     ~-2.30% |
| ops/sec     |             7,999,051              |  7,819,546          
     |     ~-2.24% |

**Loops = 10,000,000**
| Metric        | W/O Generic Framework    | With Generic Framework    | 
Improvement |
|----------|-----------------------:|-----------------------:|------------:|
| usecs/op   |              0.124613              | 0.127426            
   |     ~-2.26% |
| ops/sec     |             8,024,827              |  7,847,735          
     |     ~-2.21% |

**Overall (aggregated across all runs)**
| Metric         | W/O Generic Framework   | With Generic Framework    | 
Improvement |
| ---------- | 
---------------------:|-----------------------:|------------:|
| Total time    |           1.384 [sec]            |           1.415 
[sec]               |     ~-2.27% |
| usecs/op     |              0.124656            | 0.127480            
   |     ~-2.27% |
| ops/sec       |             8,022,098            |  7,844,423          
     |     ~-2.21% |

A 2% performance degradation was observed with the perf bench syscall.


  * Results for hackbench


| Metric        | W/O Generic Framework    | With Generic Framework   | 
Improvement |
|----------|---------------------- :|-----------------------:|------------:|
| Min Time   | 142.055 (sec).                   | 141.699 (sec)         
        | 0.25%
| Max Time  | 143.791 (sec).                   | 143.206 (sec)           
      | 0.41%
| Avg Time   | 142.925 (sec)                    | 142.472 (sec)         
        | 0.32%

So overall 0.3 % improvement is observed across 10 runs.

Please add below tag for the patch set.

Tested-by: Samir M <samir at linux.ibm.com>
Thank You !!


Regards,
Samir.
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