linux-kernel - Re: [PATCH 1/1] x86: replace cpu_up hard-coded mdelay with variable

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Date:	Mon, 20 Apr 2015 19:45:44 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	"Brown, Len" <len.brown@...el.com>
Cc:	Len Brown <lenb@...nel.org>, "x86@...nel.org" <x86@...nel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/1] x86: replace cpu_up hard-coded mdelay with variable


* Brown, Len <len.brown@...el.com> wrote:

> > What's the cutoff for 'modern hardware' - which CPUs stopped requiring
> > the delay?
> 
> This is the topic of ongoing research, and I'm not ready to send
> the patch setting a new default until I've heard back from a few more HW people.
> 
> Every system I've tested appears to work with delay 0.
> Were I to guess, I'd venture that every
> system that runs an X86_64 kernel might count as "modern" -- even
> the 2005 AMD Turion laptop I've got in the bone pile.

Could we use the apic version as a cutoff perhaps?

It would be nice to 'automatically' include modern 32-bit x86 systems 
as well.

Any failure here would be relatively easy to bisect to, so we might as 
well guess a bit and refine the quirk condition if needed?

Thanks,

	Ingo
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