linux-kernel - Re: [PATCH 1/4] irqchip: sifive-plic: Pre-compute context hart base and enable base

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Message-ID: <CAAhSdy1dYGShvtUEdDARw_8viC5P5MdMLBQOhe56nu6TMNgGaA@mail.gmail.com>
Date:   Mon, 12 Nov 2018 09:57:02 +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 1/4] irqchip: sifive-plic: Pre-compute context hart base
 and enable base

On Fri, Nov 9, 2018 at 2:12 PM Christoph Hellwig <hch@...radead.org> wrote:
>
> On Mon, Oct 22, 2018 at 05:15:14PM +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
>
> Why?

This is micro-optimizations. We don't need to re-compute
hart base and hart enable base everytime.

>
> > 3. Have enable lock for each context handler instead
> > of global plic_toggle_lock
>
> Why?  Also even if you want this it should be a separate patch.

Well, the PLIC register space it a bit strange.

Most PLIC context specific registers are in one place
except context IRQ enable registers which are part of
global registers.

To handle this, we had a global plic_toggle_lock which
was taken whenever PLIC driver touched context IRQ
enable registers. Instead of this, we can have per-context
IRQ enable lock for more granular locking.

Later when we implement IRQ set_affinity, we touch
IRQ enable registers of each context whenever IRQ
affinity changes. This fine grained IRQ enable locking
helps when IRQ load-balancer is changing affinity of
different IRQs parallely on separate cores. Again this
is a micro-optimization.

>
> >  #define PRIORITY_BASE                        0
> > -#define     PRIORITY_PER_ID          4
> > +#define PRIORITY_PER_ID                      4
>
> Also please drop the random whitespace changes.

Instead of dropping I will make it separate patch because
we are replacing "\t" between #define and define_name
with a space.

Regards,
Anup