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From: Peter Zijlstra <peterz@infradead.org>
To: Yury Norov <yury.norov@gmail.com>
Cc: linux-kernel@vger.kernel.org,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Andrew Morton <akpm@linux-foundation.org>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Paul E . McKenney" <paulmck@kernel.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	Dmitry Vyukov <dvyukov@google.com>,
	Valentin Schneider <vschneid@redhat.com>,
	Sander Vanheule <sander@svanheule.net>,
	Alexey Klimov <klimov.linux@gmail.com>,
	Eric Biggers <ebiggers@google.com>
Subject: Re: [PATCH v2 1/5] smp: don't declare nr_cpu_ids if NR_CPUS == 1
Date: Tue, 6 Sep 2022 16:36:39 +0200	[thread overview]
Message-ID: <Yxda9/XP85D1sR39@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <YxdT5w9Qd5SxK1wl@yury-laptop>

On Tue, Sep 06, 2022 at 07:06:31AM -0700, Yury Norov wrote:
> On Tue, Sep 06, 2022 at 10:53:53AM +0200, Peter Zijlstra wrote:
> > On Mon, Sep 05, 2022 at 04:08:16PM -0700, Yury Norov wrote:
> > > SMP and NR_CPUS are independent options, hence nr_cpu_ids may be
> > > declared even if NR_CPUS == 1, which is useless.
> > 
> > I'm thikning you're fixing the wrong problem here.
> 
> I'm removing dead code. If NR_CPUS == 1, nr_cpu_ids does exist, exported
> as an interface variable, but never normally reached, because in some
> other piece of code (not even in smp.h) it's declared conditionally. 

Can't you simply disallow NR_CPUS==1 for SMP builds? It doesn't make
sense anyway.

> > Why do we need extra source complexity for this?
> 
> To have effective code generation for UP builds.

Again, who cares... isn't it hard to find actual UP chips these days?

It was suggested the other day we remove a whole bunch of SMP=n code and
unconditionally use SMP code, even if its pointless on UP just to make
the source simpler.

  reply	other threads:[~2022-09-06 15:26 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-05 23:08 [PATCH v2 0/5] cpumask: cleanup nr_cpu_ids vs nr_cpumask_bits mess Yury Norov
2022-09-05 23:08 ` [PATCH v2 1/5] smp: don't declare nr_cpu_ids if NR_CPUS == 1 Yury Norov
2022-09-06  8:53   ` Peter Zijlstra
2022-09-06 14:06     ` Yury Norov
2022-09-06 14:36       ` Peter Zijlstra [this message]
2022-09-06 15:01         ` Andy Shevchenko
2022-09-06 17:53           ` Peter Zijlstra
2022-09-06 15:07         ` Yury Norov
2022-09-07  8:02         ` David Laight
2022-09-05 23:08 ` [PATCH v2 2/5] smp: add set_nr_cpu_ids() Yury Norov
2022-09-05 23:08 ` [PATCH v2 3/5] lib/cpumask: delete misleading comment Yury Norov
2022-09-05 23:08 ` [PATCH v2 4/5] lib/cpumask: deprecate nr_cpumask_bits Yury Norov
2022-09-05 23:08 ` [PATCH v2 5/5] lib/cpumask: add FORCE_NR_CPUS config option Yury Norov
2022-10-18  8:21   ` Geert Uytterhoeven
2022-10-18 13:15     ` Geert Uytterhoeven
2022-10-18 13:15       ` Geert Uytterhoeven
2022-10-18 13:41       ` Andreas Schwab
2022-10-18 13:41         ` Andreas Schwab
2022-10-18 13:50         ` Geert Uytterhoeven
2022-10-18 13:50           ` Geert Uytterhoeven
2022-10-18 14:35           ` Yury Norov
2022-10-18 14:35             ` Yury Norov
2022-10-18 14:44             ` Andy Shevchenko
2022-10-18 14:44               ` Andy Shevchenko
2022-10-18 14:59               ` Yury Norov
2022-10-18 14:59                 ` Yury Norov
2022-10-18 15:15                 ` Geert Uytterhoeven
2022-10-18 15:15                   ` Geert Uytterhoeven
2022-10-18 16:16                   ` Yury Norov
2022-10-18 16:16                     ` Yury Norov
2022-10-19  6:58                     ` Geert Uytterhoeven
2022-10-19  6:58                       ` Geert Uytterhoeven
2022-09-06  8:55 ` [PATCH v2 0/5] cpumask: cleanup nr_cpu_ids vs nr_cpumask_bits mess Peter Zijlstra
2022-09-06 12:06   ` Valentin Schneider
2022-09-06 14:38     ` Peter Zijlstra
2022-09-06 15:45       ` Valentin Schneider
2022-09-06 16:26         ` Yury Norov
2022-09-06 14:48     ` Yury Norov
2022-09-06 14:35   ` Yury Norov
2022-09-15 14:45 ` Yury Norov

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