linux-kernel - Re: [RFC PATCH] riscv: export cpu/freq invariant to scheduler

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Date:   Wed, 22 Mar 2023 09:03:45 +0100
From:   Andrew Jones <ajones@...tanamicro.com>
To:     Song Shuai <suagrfillet@...il.com>
Cc:     paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, conor.dooley@...rochip.com,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] riscv: export cpu/freq invariant to scheduler

On Wed, Mar 22, 2023 at 02:18:56PM +0800, Song Shuai wrote:
> RISC-V now manages CPU topology using arch_topology which provides
> CPU capacity and frequency related interfaces to access the cpu/freq
> invariant in possible heterogeneous or DVFS-enabled platforms.
> 
> Here adds topology.h file to export the arch_topology interfaces for
> replacing the scheduler's constant-based cpu/freq invariant accounting.
> 
> Signed-off-by: Song Shuai <suagrfillet@...il.com>
> ---
>  arch/riscv/include/asm/topology.h | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
>  create mode 100644 arch/riscv/include/asm/topology.h
> 
> diff --git a/arch/riscv/include/asm/topology.h b/arch/riscv/include/asm/topology.h
> new file mode 100644
> index 000000000000..14bbd2472af6
> --- /dev/null
> +++ b/arch/riscv/include/asm/topology.h
> @@ -0,0 +1,19 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __ASM_RISCV_TOPOLOGY_H
> +#define __ASM_RISCV_TOPOLOGY_H

riscv uses a single leading underscore.

> +
> +#include <linux/arch_topology.h>
> +
> +/* Replace task scheduler's default frequency-invariant accounting */
> +#define arch_scale_freq_tick topology_scale_freq_tick
> +#define arch_set_freq_scale topology_set_freq_scale
> +#define arch_scale_freq_capacity topology_get_freq_scale
> +#define arch_scale_freq_invariant topology_scale_freq_invariant
> +
> +/* Replace task scheduler's default cpu-invariant accounting */
> +#define arch_scale_cpu_capacity topology_get_cpu_scale
> +#define arch_update_cpu_topology topology_update_cpu_topology
> +
> +
> +#include <asm-generic/topology.h>
> +#endif /* __ASM_RISCV_TOPOLOGY_H */
> -- 
> 2.20.1
>

This looks reasonable, at least from a "do what arm64 does" type of
perspective. Why the RFC? Is it not tested?

Also, if you repost, could please neaten it up a bit? Aligning all
the defines would help and removing the extra blank line. Finally,
why wasn't the "/* Enable topology flag updates */" comment also
lifted from arm64 like the others?

Thanks,
drew