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

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Message-ID: <20090629091528.GB9724@elte.hu>
Date:	Mon, 29 Jun 2009 11:15:28 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Luming Yu <luming.yu@...il.com>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	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:

> Please note this is deep-C-state related. C state does add extra 
> latency.. but I don't know how much...

ok, so if each of the CPUs has to be brought out of deep-C and with 
each one 50-100 usecs a pop one could see the total time taking more 
than 1000 usecs. That would explain the hang.

	Ingo
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