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

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Message-ID: <4E91F82E.4080007@linux.vnet.ibm.com>
Date:	Mon, 10 Oct 2011 01:08:22 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Borislav Petkov <borislav.petkov@....com>
CC:	Ingo Molnar <mingo@...e.hu>, 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 10/09/2011 04:57 PM, Borislav Petkov wrote:
> 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
>  */
> 
Oh, ok.. Thank you for pointing it out.

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

I'll post the patch with the correct comment style, if that would make
things easier.
-- 
Regards,
Srivatsa S. Bhat  <srivatsa.bhat@...ux.vnet.ibm.com>
Linux Technology Center,
IBM India Systems and Technology Lab
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