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

From: Anup Patel <anup@brainfault.org>
To: Marc Zyngier <maz@kernel.org>
Cc: Anup Patel <anup.patel@wdc.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Palmer Dabbelt <palmerdabbelt@google.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Rob Herring <robh+dt@kernel.org>,
	Atish Patra <atish.patra@wdc.com>,
	Alistair Francis <Alistair.Francis@wdc.com>,
	linux-riscv <linux-riscv@lists.infradead.org>,
	"linux-kernel@vger.kernel.org List"
	<linux-kernel@vger.kernel.org>, DTML <devicetree@vger.kernel.org>
Subject: Re: [RFC PATCH v1 04/10] RISC-V: Use IPIs for remote TLB flush when possible
Date: Sun, 13 Jun 2021 17:58:39 +0530	[thread overview]
Message-ID: <CAAhSdy1-VbEwmWbYzB4KmCK3HjDXzi5-3S+9BS-D3o6q0iOY9g@mail.gmail.com> (raw)
In-Reply-To: <87a6nut8h9.wl-maz@kernel.org>

On Sun, Jun 13, 2021 at 3:03 PM Marc Zyngier <maz@kernel.org> wrote:
>
> On Sat, 12 Jun 2021 17:04:16 +0100,
> Anup Patel <anup.patel@wdc.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@wdc.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.