linux-kernel - Re: [RFC patch] Use IPI_shortcut for lapic timer broadcast

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Date:	Mon, 29 Jun 2009 09:20:47 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Luming Yu <luming.yu@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, suresh.b.siddha@...el.com,
	venkatesh.pallipadi@...el.com,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC patch] Use IPI_shortcut for lapic timer broadcast


* Luming Yu <luming.yu@...il.com> wrote:

> Hello,
> 
> We need to use IPI shortcut to send lapic timer broadcast
> to avoid the latency of sending IPI one bye one on systems with many
> logical processors when NO_HZ is disabled.
> Without this patch,I have seen upstream kernel with RHEL 5 kernel
> config boot hang .

hm, that might be a valid optimization - but why does the lack of 
this optimization result in a hang?

	Ingo
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