Re: [RFC 0/2] riscv: Idle thread using Zawrs extension

From: "Christoph Müllner" <christoph.muellner@vrull.eu>
To: Xu Lu <luxu.kernel@bytedance.com>
Cc: paul.walmsley@sifive.com, palmer@dabbelt.com,
	aou@eecs.berkeley.edu,  andy.chiu@sifive.com, guoren@kernel.org,
	linux-riscv@lists.infradead.org,  linux-kernel@vger.kernel.org,
	lihangjing@bytedance.com,  dengliang.1214@bytedance.com,
	xieyongji@bytedance.com,  chaiwen.cc@bytedance.com,
	Andrew Jones <ajones@ventanamicro.com>,
	 Conor Dooley <conor.dooley@microchip.com>
Subject: Re: [RFC 0/2] riscv: Idle thread using Zawrs extension
Date: Thu, 18 Apr 2024 14:26:12 +0200	[thread overview]
Message-ID: <CAEg0e7gDk6SFRh4oF0KsA7xZoMr7RuZXFWL8qD7rmM2cBDLwcg@mail.gmail.com> (raw)
In-Reply-To: <20240418114942.52770-1-luxu.kernel@bytedance.com>

On Thu, Apr 18, 2024 at 1:50 PM Xu Lu <luxu.kernel@bytedance.com> wrote:
>
> This patch series introduces a new implementation of idle thread using
> Zawrs extension.

This overlaps with the following series:
  https://lore.kernel.org/all/20240315134009.580167-7-ajones@ventanamicro.com/

BR
Christoph

>
> The Zawrs[0] extension introduces two new instructions named WRS.STO and
> WRS.NTO in RISC-V. When software registers a reservation set using LR
> instruction, a subsequent WRS.STO or WRS.NTO instruction will cause the
> hart to stall in a low-power state until a store happens to the
> reservation set or an interrupt becomes pending. The difference between
> these two instructions is that WRS.STO will terminate stall after an
> implementation-defined timeout while WRS.NTO won't.
>
> This patch series implements idle thread using WRS.NTO instruction.
> Besides, we found there is no need to send a real IPI to wake up an idle
> CPU. Instead, we write IPI information to the reservation set of an idle
> CPU to wake it up and let it handle IPI quickly, without going through
> tranditional interrupt handling routine.
>
> [0] https://github.com/riscv/riscv-zawrs/blob/main/zawrs.adoc
>
> Xu Lu (2):
>   riscv: process: Introduce idle thread using Zawrs extension
>   riscv: Use Zawrs to accelerate IPI to idle cpu
>
>  arch/riscv/Kconfig                 |  24 +++++++
>  arch/riscv/include/asm/cpuidle.h   |  11 +---
>  arch/riscv/include/asm/hwcap.h     |   1 +
>  arch/riscv/include/asm/processor.h |  31 +++++++++
>  arch/riscv/include/asm/smp.h       |  14 ++++
>  arch/riscv/kernel/cpu.c            |   5 ++
>  arch/riscv/kernel/cpufeature.c     |   1 +
>  arch/riscv/kernel/process.c        | 102 ++++++++++++++++++++++++++++-
>  arch/riscv/kernel/smp.c            |  39 +++++++----
>  9 files changed, 205 insertions(+), 23 deletions(-)
>
> --
> 2.20.1
>
>
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