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

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Message-ID: <20190430121148.GV2623@hirez.programming.kicks-ass.net>
Date:   Tue, 30 Apr 2019 14:11:48 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yuyang Du <duyuyang@...il.com>
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

On Fri, Apr 26, 2019 at 02:57:37PM +0800, Yuyang Du wrote:
> 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?

Frederic? My understanding was that he really was going to split the
whole thing. The moment you allow masking individual soft vectors, you
get per-vector dependency chains.