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

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Date:	Mon, 20 Apr 2015 12:37:52 +0000
From:	"Brown, Len" <len.brown@...el.com>
To:	Ingo Molnar <mingo@...nel.org>, Len Brown <lenb@...nel.org>
CC:	"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

> 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.

> Also, is there any public document where the no-delay is specified for
> 'modern hardware'?

Unfortunately only the converse is true.  There is an ancient document specifying
that the delay may be necessary.

cheers,
-Len

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