linux-kernel - Re: [PATCH 19/28] locking/lockdep: Optimize irq usage check when marking lock usage bit

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Message-ID: <CAHttsrY4jK2cayBE8zNCSJKDAkzLiBb40GVfQHpJi2YK1nEZaQ@mail.gmail.com>
Date:   Fri, 26 Apr 2019 14:57:37 +0800
From:   Yuyang Du <duyuyang@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     will.deacon@....com, Ingo Molnar <mingo@...nel.org>,
        Bart Van Assche <bvanassche@....org>, ming.lei@...hat.com,
        Frederic Weisbecker <frederic@...nel.org>, tglx@...utronix.de,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 19/28] locking/lockdep: Optimize irq usage check when
 marking lock usage bit

Thanks for review.

On Fri, 26 Apr 2019 at 03:32, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Wed, Apr 24, 2019 at 06:19:25PM +0800, Yuyang Du wrote:
>
> After only a quick read of these next patches; this is the one that
> worries me most.
>
> You did mention Frederic's patches, but I'm not entirely sure you're
> aware why he's doing them. He's preparing to split the softirq state
> into one state per softirq vector.
>
> See here:
>
>   https://lkml.kernel.org/r/20190228171242.32144-14-frederic@kernel.org
>   https://lkml.kernel.org/r/20190228171242.32144-15-frederic@kernel.org
>
> IOW he's going to massively explode this storage.

If I understand correctly, he is not going to.

First of all, we can divide the whole usage thing into tracking and checking.

Frederic's fine-grained soft vector state is applied to usage
tracking, i.e., which specific vectors a lock is used or enabled.

But for usage checking, which vectors are does not really matter. So,
the current size of the arrays and bitmaps are good enough. Right?