Re: [PATCH v1 0/7] perf bench: Add qspinlock benchmark

[Mark Rutland <mark.rutland@arm.com>]

On Mon, Jul 28, 2025 at 07:26:33PM -0700, Yuzhuo Jing wrote:
> As an effort to improve the perf bench subcommand, this patch series
> adds benchmark for the kernel's queued spinlock implementation.
> 
> This series imports necessary kernel definitions such as atomics,
> introduces userspace per-cpu adapter, and imports the qspinlock
> implementation from the kernel tree to tools tree, with minimum
> adaptions.

Who is this intended to be useful for, and when would they use this?

This doesn't serve as a benchmark of the host kernel, since it tests
whatever stale copy of the qspinlock code was built into the perf
binary.

I can understand that being able to test the code in userspace may be
helpful when making some changes, but why does this need to be built
into the perf tool?

Mark.

> This subcommand enables convenient commands to investigate the
> performance of kernel lock implementations, such as using sampling:
> 
>     perf record -- ./perf bench sync qspinlock -t5
>     perf report
> 
> Yuzhuo Jing (7):
>   tools: Import cmpxchg and xchg functions
>   tools: Import smp_cond_load and atomic_cond_read
>   tools: Partial import of prefetch.h
>   tools: Implement userspace per-cpu
>   perf bench: Import qspinlock from kernel
>   perf bench: Add 'bench sync qspinlock' subcommand
>   perf bench sync: Add latency histogram functionality
> 
>  tools/arch/x86/include/asm/atomic.h           |  14 +
>  tools/arch/x86/include/asm/cmpxchg.h          | 113 +++++
>  tools/include/asm-generic/atomic-gcc.h        |  47 ++
>  tools/include/asm/barrier.h                   |  58 +++
>  tools/include/linux/atomic.h                  |  27 ++
>  tools/include/linux/compiler_types.h          |  30 ++
>  tools/include/linux/percpu-simulate.h         | 128 ++++++
>  tools/include/linux/prefetch.h                |  41 ++
>  tools/perf/bench/Build                        |   2 +
>  tools/perf/bench/bench.h                      |   1 +
>  .../perf/bench/include/mcs_spinlock-private.h | 115 +++++
>  tools/perf/bench/include/mcs_spinlock.h       |  19 +
>  tools/perf/bench/include/qspinlock-private.h  | 204 +++++++++
>  tools/perf/bench/include/qspinlock.h          | 153 +++++++
>  tools/perf/bench/include/qspinlock_types.h    |  98 +++++
>  tools/perf/bench/qspinlock.c                  | 411 ++++++++++++++++++
>  tools/perf/bench/sync.c                       | 329 ++++++++++++++
>  tools/perf/builtin-bench.c                    |   7 +
>  tools/perf/check-headers.sh                   |  32 ++
>  19 files changed, 1829 insertions(+)
>  create mode 100644 tools/include/linux/percpu-simulate.h
>  create mode 100644 tools/include/linux/prefetch.h
>  create mode 100644 tools/perf/bench/include/mcs_spinlock-private.h
>  create mode 100644 tools/perf/bench/include/mcs_spinlock.h
>  create mode 100644 tools/perf/bench/include/qspinlock-private.h
>  create mode 100644 tools/perf/bench/include/qspinlock.h
>  create mode 100644 tools/perf/bench/include/qspinlock_types.h
>  create mode 100644 tools/perf/bench/qspinlock.c
>  create mode 100644 tools/perf/bench/sync.c
> 
> -- 
> 2.50.1.487.gc89ff58d15-goog
>