linux-kernel - Re: [PATCH v4 0/3] sched: make migrate_enable/migrate

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Message-ID: <5923659.DvuYhMxLoT@7940hx>
Date: Mon, 15 Sep 2025 09:49:58 +0800
From: Menglong Dong <menglong.dong@...ux.dev>
To: peterz@...radead.org
Cc: ast@...nel.org, mingo@...hat.com, juri.lelli@...hat.com,
 vincent.guittot@...aro.org, dietmar.eggemann@....com, rostedt@...dmis.org,
 bsegall@...gle.com, mgorman@...e.de, vschneid@...hat.com,
 daniel@...earbox.net, john.fastabend@...il.com, andrii@...nel.org,
 martin.lau@...ux.dev, eddyz87@...il.com, song@...nel.org,
 yonghong.song@...ux.dev, kpsingh@...nel.org, sdf@...ichev.me,
 haoluo@...gle.com, jolsa@...nel.org, tzimmermann@...e.de,
 simona.vetter@...ll.ch, jani.nikula@...el.com, linux-kernel@...r.kernel.org,
 bpf@...r.kernel.org
Subject: Re: [PATCH v4 0/3] sched: make migrate_enable/migrate_disable inline

On 2025/8/28 14:03 Menglong Dong <menglong.dong@...ux.dev> write:
> In this series, we make migrate_enable/migrate_disable inline to obtain
> better performance in some case.
> 
> In the first patch, we add the macro "COMPILE_OFFSETS" to all the
> asm-offset.c to avoid circular dependency in the 2nd patch.
> 
> In the 2nd patch, we generate the offset of nr_pinned in "struct rq" with
> rq-offsets.c, as the "struct rq" is defined internally and we need to
> access the "nr_pinned" field in migrate_enable and migrate_disable. Then,
> we move the definition of migrate_enable/migrate_disable from
> kernel/sched/core.c to include/linux/sched.h.
> 
> In the 3rd patch, we fix some typos in include/linux/preempt.h.

Hi, everyone. Do we have any thoughts on this series?

Thanks!
Menglong Dong

> 
> One of the beneficiaries of this series is BPF trampoline. Without this
> series, the migrate_enable/migrate_disable is hot when we run the
> benchmark for FENTRY, FEXIT, MODIFY_RETURN, etc:
> 
>   54.63% bpf_prog_2dcccf652aac1793_bench_trigger_fentry [k]
>                  bpf_prog_2dcccf652aac1793_bench_trigger_fentry
>   10.43% [kernel] [k] migrate_enable
>   10.07% bpf_trampoline_6442517037 [k] bpf_trampoline_6442517037
>   8.06% [kernel] [k] __bpf_prog_exit_recur
>   4.11% libc.so.6 [.] syscall
>   2.15% [kernel] [k] entry_SYSCALL_64
>   1.48% [kernel] [k] memchr_inv
>   1.32% [kernel] [k] fput
>   1.16% [kernel] [k] _copy_to_user
>   0.73% [kernel] [k] bpf_prog_test_run_raw_tp
> 
> Before this patch, the performance of BPF FENTRY is:
> 
>   fentry         :  113.030 ± 0.149M/s
>   fentry         :  112.501 ± 0.187M/s
>   fentry         :  112.828 ± 0.267M/s
>   fentry         :  115.287 ± 0.241M/s
> 
> After this patch, the performance of BPF FENTRY increases to:
> 
>   fentry         :  143.644 ± 0.670M/s
>   fentry         :  149.764 ± 0.362M/s
>   fentry         :  149.642 ± 0.156M/s
>   fentry         :  145.263 ± 0.221M/s
> 
> Changes since V3:
> * some modification on the 2nd patch, as Alexei advised:
>  - rename CREATE_MIGRATE_DISABLE to INSTANTIATE_EXPORTED_MIGRATE_DISABLE
>  - add document for INSTANTIATE_EXPORTED_MIGRATE_DISABLE
> 
> Changes since V2:
> * some modification on the 2nd patch, as Peter advised:
>   - don't export runqueues, define migrate_enable and migrate_disable in
>     kernel/sched/core.c and use them for kernel modules instead
>   - define the macro this_rq_pinned()
>   - add some comment for this_rq_raw()
> 
> Changes since V1:
> * use PERCPU_PTR() for this_rq_raw() if !CONFIG_SMP in the 2nd patch
> 
> Menglong Dong (3):
>   arch: add the macro COMPILE_OFFSETS to all the asm-offsets.c
>   sched: make migrate_enable/migrate_disable inline
>   sched: fix some typos in include/linux/preempt.h
> 
>  Kbuild                               |  13 ++-
>  arch/alpha/kernel/asm-offsets.c      |   1 +
>  arch/arc/kernel/asm-offsets.c        |   1 +
>  arch/arm/kernel/asm-offsets.c        |   2 +
>  arch/arm64/kernel/asm-offsets.c      |   1 +
>  arch/csky/kernel/asm-offsets.c       |   1 +
>  arch/hexagon/kernel/asm-offsets.c    |   1 +
>  arch/loongarch/kernel/asm-offsets.c  |   2 +
>  arch/m68k/kernel/asm-offsets.c       |   1 +
>  arch/microblaze/kernel/asm-offsets.c |   1 +
>  arch/mips/kernel/asm-offsets.c       |   2 +
>  arch/nios2/kernel/asm-offsets.c      |   1 +
>  arch/openrisc/kernel/asm-offsets.c   |   1 +
>  arch/parisc/kernel/asm-offsets.c     |   1 +
>  arch/powerpc/kernel/asm-offsets.c    |   1 +
>  arch/riscv/kernel/asm-offsets.c      |   1 +
>  arch/s390/kernel/asm-offsets.c       |   1 +
>  arch/sh/kernel/asm-offsets.c         |   1 +
>  arch/sparc/kernel/asm-offsets.c      |   1 +
>  arch/um/kernel/asm-offsets.c         |   2 +
>  arch/xtensa/kernel/asm-offsets.c     |   1 +
>  include/linux/preempt.h              |  11 +--
>  include/linux/sched.h                | 113 +++++++++++++++++++++++++++
>  kernel/bpf/verifier.c                |   1 +
>  kernel/sched/core.c                  |  63 ++++-----------
>  kernel/sched/rq-offsets.c            |  12 +++
>  26 files changed, 180 insertions(+), 57 deletions(-)
>  create mode 100644 kernel/sched/rq-offsets.c
> 
> -- 
> 2.51.0
> 
>