linux-kernel - RE: [PATCH] drivers: base: update cpu offline info when do hotplug

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Message-ID: <9034CBD80F070943B59700D7F8149ED9024EB81CC6@SC-VEXCH4.marvell.com>
Date:	Mon, 20 Oct 2014 00:40:48 -0700
From:	Neil Zhang <zhangwm@...vell.com>
To:	Greg KH <gregkh@...uxfoundation.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] drivers: base: update cpu offline info when do hotplug

Greg,

-----Original Message-----
From: Greg KH [mailto:gregkh@...uxfoundation.org] 
Sent: 2014年10月20日 14:48
To: Neil Zhang
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers: base: update cpu offline info when do hotplug

On Sun, Oct 19, 2014 at 11:39:23PM -0700, Neil Zhang wrote:
>> How much noise is this going to cause on a big/little system that 
>> constantly hot unplug/plugs processors all of the time?
> 
> Can you explain more what kind of noise will be introduced on a big/little system?

Have you tested this on such a machine?

I didn't have such kind of machine on hand.
Can anyone has such machine to verify it?
Thanks!

> As I know IKS on arm will use cpu_suspend way to power down a core.

Are you sure that it also doesn't use that same functionality to drop a processor to save power?

As I know it use cpu_suspend to switch out a processor in IKS and there is no cpu hotplug notifier in this procedure.

Why do you need/want this notification?  What are you going to do with this information that you don't already have?

The offline won't be updated if an in kernel hotplug governor plug in / out a core which cause the sysfs interface report a wrong status.

thanks,

greg k-h

Best Regards,
Neil Zhang