linux-kernel - Re: [PATCH] arch/x86/kernel/cpu/umwait.c

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Date:   Thu, 8 Aug 2019 17:44:39 -0700
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Valdis Klētnieks <valdis.kletnieks@...edu>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arch/x86/kernel/cpu/umwait.c - remove unused variable

On Thu, Aug 08, 2019 at 10:32:38PM +0200, Thomas Gleixner wrote:
> Valdis,
> 
> On Thu, 8 Aug 2019, Valdis Klētnieks wrote:
> > On Thu, 08 Aug 2019 22:04:03 +0200, Thomas Gleixner said: It isn't 
> > clear that whatever is doing the device_initcall()s will be able to 
> > do any reasonable recovery if we return an error, so any error 
> > recovery is going to have to happen before the function returns. It 
> > might make sense to do an 'if (ret) return;' before going further in 
> > the function, but given the comment a few lines further down about 
> > ignoring errors, it was apparently considered more important to 
> > struggle through and register stuff in sysfs even if umwait was 
> > broken....
> 
> I missed that when going through it.
> 
> The right thing to do is to have a cpu_offline callback which clears 
> the umwait MSR. That covers also the failure in the cpu hotplug setup. 
> Then handling an error return makes sense and keeps everything in a 
> workable shape.

When cpu is offline, the MSR won't be used. We don't need to clear it, right?

Thanks.

-Fenghua