linux-kernel - Re: [RFC PATCH] x86: Add safe_udelay() and safe

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Message-ID: <alpine.DEB.2.00.1101140846340.2423@router.home>
Date:	Fri, 14 Jan 2011 08:46:46 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Yinghai Lu <yinghai@...nel.org>
cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Greg KH <greg@...ah.com>,
	Jason Wessel <jason.wessel@...driver.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [RFC PATCH] x86: Add safe_udelay() and safe_msleep()

On Thu, 13 Jan 2011, Yinghai Lu wrote:

> > Or have a reasonable default for lpj ...
>
> x86 udelay is using percpu cpu_data.loops_per_jiffy, and it is not set yet.
>
> when x86 boot with earlyprintk=dbgp, that early console is loaded quite before setup_percpu_areas()
>
> maybe something like this could workaround it, if cpu_data(0) can be used before setup_percpu_areas().
>
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index d3cfe26..333694a 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -734,6 +734,7 @@ void __init setup_arch(char **cmdline_p)
>
>         early_trap_init();
>         early_cpu_init();
> +       cpu_data(0).loops_per_jiffy = loops_per_jiffy;
>         early_ioremap_init();
>
>         setup_olpc_ofw_pgd();

That could work.

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