linux-kernel - Re: [PATCH 02/16] dept: Implement Dept(Dependency Tracker)

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Date:   Fri, 18 Feb 2022 15:09:26 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     torvalds@...ux-foundation.org, damien.lemoal@...nsource.wdc.com,
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Subject: Re: [PATCH 02/16] dept: Implement Dept(Dependency Tracker)

On Thu, Feb 17, 2022 at 12:36:56PM -0500, Steven Rostedt wrote:
> > +struct dept_ecxt;
> > +struct dept_iecxt {
> > +	struct dept_ecxt *ecxt;
> > +	int enirq;
> > +	bool staled; /* for preventing to add a new ecxt */
> > +};
> > +
> > +struct dept_wait;
> > +struct dept_iwait {
> > +	struct dept_wait *wait;
> > +	int irq;
> > +	bool staled; /* for preventing to add a new wait */
> > +	bool touched;
> > +};
> 
> Nit. It makes it easier to read (and then review) if structures are spaced
> where their fields are all lined up:
> 
> struct dept_iecxt {
> 	struct dept_ecxt		*ecxt;
> 	int				enirq;
> 	bool				staled;
> };
> 
> struct dept_iwait {
> 	struct dept_wait		*wait;
> 	int				irq;
> 	bool				staled;
> 	bool				touched;
> };
> 
> See, the fields stand out, and is nicer on the eyes. Especially for those
> of us that are getting up in age, and our eyes do not work as well as they
> use to ;-)

Sure! I will apply this.

> > + * ---
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License as published by
> > + * the Free Software Foundation; either version 2 of the License, or
> > + * (at your ootion) any later version.
> > + *
> > + * This program is distributed in the hope that it will be useful, but
> > + * WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> > + * General Public License for more details.
> > + *
> > + * You should have received a copy of the GNU General Public License
> > + * along with this program; if not, you can access it online at
> > + * http://www.gnu.org/licenses/gpl-2.0.html.
> 
> The SPDX at the top of the file is all that is needed. Please remove this
> boiler plate. We do not use GPL boiler plates in the kernel anymore. The
> SPDX code supersedes that.

Thank you for informing it!

> > +/*
> > + * Can use llist no matter whether CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG is
> > + * enabled because DEPT never race with NMI by nesting control.
> 
>                          "never races with"

Good eyes!

> Although, I'm confused by what you mean with "by nesting control".

I should've expressed it more clearly. It meant NMI and other contexts
never run inside of Dept concurrently in the same CPU by preventing
reentrance.

> > +static void initialize_class(struct dept_class *c)
> > +{
> > +	int i;
> > +
> > +	for (i = 0; i < DEPT_IRQS_NR; i++) {
> > +		struct dept_iecxt *ie = &c->iecxt[i];
> > +		struct dept_iwait *iw = &c->iwait[i];
> > +
> > +		ie->ecxt = NULL;
> > +		ie->enirq = i;
> > +		ie->staled = false;
> > +
> > +		iw->wait = NULL;
> > +		iw->irq = i;
> > +		iw->staled = false;
> > +		iw->touched = false;
> > +	}
> > +	c->bfs_gen = 0U;
> 
> Is the U really necessary?

I was just wondering if it's really harmful? I want to leave this if
it's harmless because U let us guess the data type of ->bfs_gen correctly
at a glance. Or am I missing some reason why I should fix this?

Thank you very much, Steven.