linux-kernel - RE: [PATCH 0/8] Online/offline BSP on x86

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Message-ID: <493994B35A117E4F832F97C4719C4C040136F7CCBD@orsmsx505.amr.corp.intel.com>
Date:	Wed, 5 Oct 2011 13:29:12 -0700
From:	"Yu, Fenghua" <fenghua.yu@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	H Peter Anvin <hpa@...or.com>,
	"Luck, Tony" <tony.luck@...el.com>,
	"Mallick, Asit K" <asit.k.mallick@...el.com>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	"Brown, Len" <len.brown@...el.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 0/8] Online/offline BSP on x86



> -----Original Message-----
> From: Peter Zijlstra [mailto:peterz@...radead.org]
> Sent: Wednesday, October 05, 2011 12:28 PM
> To: Yu, Fenghua
> Cc: Ingo Molnar; Thomas Gleixner; H Peter Anvin; Luck, Tony; Mallick,
> Asit K; Siddha, Suresh B; Brown, Len; linux-kernel
> Subject: RE: [PATCH 0/8] Online/offline BSP on x86
> 
> On Wed, 2011-10-05 at 12:22 -0700, Yu, Fenghua wrote:
> >
> > > -----Original Message-----
> > > From: Peter Zijlstra [mailto:peterz@...radead.org]
> > > Sent: Wednesday, October 05, 2011 12:17 PM
> > > To: Yu, Fenghua
> > > Cc: Ingo Molnar; Thomas Gleixner; H Peter Anvin; Zwane Mwaikambo;
> Luck,
> > > Tony; Mallick, Asit K; Siddha, Suresh B; Len Brown; linux-kernel
> > > Subject: Re: [PATCH 0/8] Online/offline BSP on x86
> > >
> > > On Wed, 2011-10-05 at 09:39 -0700, Fenghua Yu wrote:
> > > >
> > > > BSP or CPU0 has been the last obstacle to CPU hotplug on x86.
> This
> > > patch set
> > > > implements BSP online and offline and removes this obstacle to
> CPU
> > > hotplug.
> > >
> > > Are you talking about physical cpu hotplug on x86? And you need to
> > > offline the BSP so you can replace socket0 ?
> >
> >
> > This patch set is for BSP online/offline.
> 
> Yes, I got that part. Why do you care?

I can think of two reasons for bsp offline/online:

1. RAS needs the feature. If socket0 needs to be hotplugged for any reason (any thread on socket0 is bad, shared cache issue, uncore issue, etc), CPU0 is required to be offlined.

2. CPU0 is symmetrical to other CPU's. There is no specific reason why it shouldn't be offlined except BIOS requirements.

Thanks.

-Fenghua