linux-kernel - Re: [RFC PATCH v1 04/10] RISC-V: Use IPIs for remote TLB flush when possible

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Date:   Sun, 13 Jun 2021 17:58:39 +0530
From:   Anup Patel <anup@...infault.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Anup Patel <anup.patel@....com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Atish Patra <atish.patra@....com>,
        Alistair Francis <Alistair.Francis@....com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>
Subject: Re: [RFC PATCH v1 04/10] RISC-V: Use IPIs for remote TLB flush when possible

On Sun, Jun 13, 2021 at 3:03 PM Marc Zyngier <maz@...nel.org> wrote:
>
> On Sat, 12 Jun 2021 17:04:16 +0100,
> Anup Patel <anup.patel@....com> wrote:
> >
> > If IPI calls are injected using SBI IPI calls then remote TLB flush
> > using SBI RFENCE calls is much faster because using IPIs for remote
> > TLB flush would still endup as SBI IPI calls with extra processing
> > on kernel side.
> >
> > It is now possible to have specialized hardware (such as RISC-V AIA)
> > which allows S-mode software to directly inject IPIs without any
> > assistance from M-mode runtime firmware.
> >
> > This patch extends remote TLB flush functions to use IPIs whenever
> > underlying IPI operations are suitable for remote FENCEs.
> >
> > Signed-off-by: Anup Patel <anup.patel@....com>
> > ---
> >  arch/riscv/mm/tlbflush.c | 62 +++++++++++++++++++++++++++++++---------
> >  1 file changed, 48 insertions(+), 14 deletions(-)
> >
> > diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
> > index 720b443c4528..009c56fa102d 100644
> > --- a/arch/riscv/mm/tlbflush.c
> > +++ b/arch/riscv/mm/tlbflush.c
> > @@ -1,39 +1,73 @@
> >  // SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * TLB flush implementation.
> > + *
> > + * Copyright (c) 2021 Western Digital Corporation or its affiliates.
> > + */
>
> I find this a bit odd. You don't mention this addition in the commit
> message, and a quick look at the commits touching tlbflush.[ch]
> doesn't make the copyright assignment obvious (most commits originate
> from either SiFive or Christoph).
>
> In any way, please keep this kind of changes out of this series if
> possible, and have a separate discussion on who gets to brag about
> this code.

I agree it's unrelated change.

The commit history suggest mm/tlbflush.c was added by Christoph
and other commits after that are from Atish (Western Digital).

I will sort this out separately.

Regards,
Anup

>
> Thanks,
>
>         M.
>
> --
> Without deviation from the norm, progress is not possible.