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

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Date:	Mon, 20 Apr 2015 09:13:06 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Len Brown <lenb@...nel.org>
Cc:	x86@...nel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Len Brown <len.brown@...el.com>,
	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


* Len Brown <lenb@...nel.org> wrote:

> +config X86_INIT_MDELAY
> +	int "Milliseconds to wait to de-assert INIT upon CPU startup" if SMP
> +	range 0 10
> +	default "10"
> +	---help---
> +	  This allows you to specify how long the BSP will delay
> +	  between asserting INIT and de-asserting INIT when starting another CPU.
> +	  This delay is paid on each cpu-online operation, including boot-time,
> +	  resume from suspend, and resume from hibernate.  The the value of
> +	  10 millisec was specified by Multi-Processor Spec 1.4 in 1997.
> +	  But modern hardware does not require any delay.

What's the cutoff for 'modern hardware' - which CPUs stopped requiring 
the delay?

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

Thanks,

	Ingo
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