linux-kernel - Re: [PATCH 2/4][RFC v2] PM / sleep: Introduce arch-specific hook for disable/enable nonboot cpus

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Date:   Tue, 11 Oct 2016 17:42:51 +0200
From:   Pavel Machek <pavel@....cz>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Chen Yu <yu.c.chen@...el.com>, linux-pm@...r.kernel.org,
        x86@...nel.org, "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...e.de>,
        Brian Gerst <brgerst@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Varun Koyyalagunta <cpudebug@...ttech.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4][RFC v2] PM / sleep: Introduce arch-specific hook for
 disable/enable nonboot cpus

On Fri 2016-10-07 12:31:41, Andy Lutomirski wrote:
> On 06/25/2016 09:18 AM, Chen Yu wrote:
> >There is requirement that we need to do some arch-specific
> >operations before putting the nonboot CPUs offline/online.
> >One of the requirements comes from the hibernation resume
> >process on x86_64, we need to kick all the offlin-CPUs
> >online and offline again, in order to put them in a safe
> >state, thus to avoid possible unwilling wake up during
> >hibernation resume.
> >
> >Signed-off-by: Chen Yu <yu.c.chen@...el.com>
> >---
> > kernel/cpu.c | 12 ++++++++++++
> > 1 file changed, 12 insertions(+)
> >
> >diff --git a/kernel/cpu.c b/kernel/cpu.c
> >index d25266e..ce6e5e4 100644
> >--- a/kernel/cpu.c
> >+++ b/kernel/cpu.c
> >@@ -1017,6 +1017,16 @@ EXPORT_SYMBOL_GPL(cpu_up);
> > #ifdef CONFIG_PM_SLEEP_SMP
> > static cpumask_var_t frozen_cpus;
> >
> >+void __weak arch_disable_nonboot_cpus_pre(void)
> 
> I don't like using __weak.  It penalizes code size on architectures that
> don't hook these functions.  My preferred pattern is:
> 
> include/linux/something.h:
> 
> #include <asm/something.h>
> 
> #ifndef arch_do_xyz
> static inline void arch_do_xyz() {}
> #endif
> 
> arch/whatever/asm/something.h:
> 
> extern void arch_do_xyz();  /* or static inline... */
> #define arch_do_xyz
> 
> 
> This is totally free for architectures that don't have the hooks and it can
> potentially be inlined on architectures that do have the hooks. Everyone
> wins except that it's about five additional lines of code.

Well... 5 additional lines may be worse than few bytes in the object
file...

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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