linux-kernel - Re: [PATCH v3 1/6] irqchip: sifive-plic: Pre-compute context hart base and enable base

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Message-ID: <CAAhSdy11WFLjMGa6PVWdL1=YVQLA_nHB5kA1rBj2FFuk0dOeMw@mail.gmail.com>
Date:   Tue, 18 Dec 2018 14:00:21 +0530
From:   Anup Patel <anup@...infault.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Palmer Dabbelt <palmer@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <marc.zyngier@....com>,
        Atish Patra <atish.patra@....com>,
        linux-riscv@...ts.infradead.org,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/6] irqchip: sifive-plic: Pre-compute context hart
 base and enable base

On Mon, Dec 17, 2018 at 11:55 PM Christoph Hellwig <hch@...radead.org> wrote:
>
> On Fri, Nov 30, 2018 at 01:32:02PM +0530, Anup Patel wrote:
> > This patch does following optimizations:
> > 1. Pre-compute hart base for each context handler
> > 2. Pre-compute enable base for each context handler
> > 3. Have enable lock for each context handler instead
> > of global plic_toggle_lock
>
> All of which is pretty obvious from reading the patch.  The big question
> that needs to be answered in the changelog is why you do that.

To compute enable_base and hart_base is two integer additions and
one integer multiplication. This micro-optimization simply avoids this
repeated operations.

Regards,
Anup