linux-kernel - Re: [PATCH] CPU hotplug,x86 Microcode: Don't request microcode from userspace unnecessarily

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Date:	Sun, 9 Oct 2011 13:27:55 +0200
From:	Borislav Petkov <borislav.petkov@....com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>
CC:	Borislav Petkov <bp@...64.org>,
	"tigran@...azian.fsnet.co.uk" <tigran@...azian.fsnet.co.uk>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
	"Herrmann3, Andreas" <Andreas.Herrmann3@....com>,
	"amd64-microcode@...64.org" <amd64-microcode@...64.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Tejun Heo <tj@...nel.org>,
	Linux PM mailing list <linux-pm@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] CPU hotplug,x86 Microcode: Don't request microcode from
 userspace unnecessarily

On Sat, Oct 08, 2011 at 04:47:53PM -0400, Srivatsa S. Bhat wrote:
> Requesting the microcode from userspace *every time* when onlining CPUs
> (during a CPU hotplug operation) is unnecessary.
> 
> So, this patch ensures that once the kernel gets the microcode after booting,
> it is not freed nor invalidated when a CPU goes offline, so that it can be
> reused when that CPU comes back online, without requesting userspace for it
> again. As a result, the CPU hotplug operations become faster as well.
> 
> Tested-by: Borislav Petkov <bp@...64.org>
> Acked-by: Borislav Petkov <bp@...64.org>
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>

Good, thanks. Just a minor nitpick below.

> ---
> 
>  arch/x86/kernel/microcode_core.c |    8 +++++++-
>  1 files changed, 7 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/kernel/microcode_core.c b/arch/x86/kernel/microcode_core.c
> index f924280..3fd0189 100644
> --- a/arch/x86/kernel/microcode_core.c
> +++ b/arch/x86/kernel/microcode_core.c
> @@ -483,7 +483,13 @@ mc_cpu_callback(struct notifier_block *nb, unsigned long action, void *hcpu)
>  		sysfs_remove_group(&sys_dev->kobj, &mc_attr_group);
>  		pr_debug("CPU%d removed\n", cpu);
>  		break;
> -	case CPU_DEAD:
> +
> +	/* When a CPU goes offline, don't free up or invalidate the copy of
> +	 * the microcode in kernel memory, so that we can reuse it when the
> +	 * CPU comes back online without unnecessarily requesting the userspace
> +	 * for it again.
> +	 */
> +

Kernel comment style is in this format:

/*
 * Blabla
 * blublu
 */

@Ingo, can you please adjust it in-flight when applying?

Thanks.

-- 
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
Einsteinring 24, 85609 Dornach
GM: Alberto Bozzo
Reg: Dornach, Landkreis Muenchen
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