linux-kernel - Re: [patch]x86: spread tlb flush vector between nodes

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Message-ID: <20101013111913.GA32131@elte.hu>
Date:	Wed, 13 Oct 2010 13:19:13 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"hpa@...or.com" <hpa@...or.com>,
	"Chen, Tim C" <tim.c.chen@...el.com>
Subject: Re: [patch]x86: spread tlb flush vector between nodes


* Shaohua Li <shaohua.li@...el.com> wrote:

> On Wed, 2010-10-13 at 16:16 +0800, Andi Kleen wrote:
> > On Wed, Oct 13, 2010 at 03:41:38PM +0800, Shaohua Li wrote:
> > > +
> > > +static int tlb_cpuhp_notify(struct notifier_block *n,
> > > +		unsigned long action, void *hcpu)
> > > +{
> > > +	switch (action & 0xf) {
> > > +	case CPU_ONLINE:
> > > +	case CPU_DEAD:
> > > +		calculate_tlb_offset();
> > > +	}
> > > +	return NOTIFY_OK;
> > 
> > I don't think we really need the complexity of a notifier here.
> > In most x86 setups possible is very similar to online.
> > 
> > So I would suggest simply to compute a static mapping at boot
> > and simplify the code.
> > 
> > In theory there is a slight danger of node<->CPU numbers
> > changing with consecutive hot plug actions, but right now
> > this should not happen anyways and it would be unlikely
> > later.
>
> yes, it's unlikely. could we get the node info for a CPU before it's 
> hotplugged? Anyway, this doesn't take overhead.

It would be rather stupid to throw away the fairly simple hotplug-aware 
code you wrote and replace it with some lame boot-time calculated 
mapping just because currently it's considered rare.

Thanks,

	Ingo
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