linux-kernel - Re: [PATCH v2 1/5] smp: don't declare nr_cpu_ids if NR

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Yxda9/XP85D1sR39@hirez.programming.kicks-ass.net>
Date:   Tue, 6 Sep 2022 16:36:39 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yury Norov <yury.norov@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Sander Vanheule <sander@...nheule.net>,
        Alexey Klimov <klimov.linux@...il.com>,
        Eric Biggers <ebiggers@...gle.com>
Subject: Re: [PATCH v2 1/5] smp: don't declare nr_cpu_ids if NR_CPUS == 1

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.