From: Luming Yu <luming.yu@gmail.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: LKML <linux-kernel@vger.kernel.org>,
suresh.b.siddha@intel.com, venkatesh.pallipadi@intel.com,
Thomas Gleixner <tglx@linutronix.de>,
"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [RFC patch] Use IPI_shortcut for lapic timer broadcast
Date: Mon, 29 Jun 2009 16:04:35 +0800 [thread overview]
Message-ID: <3877989d0906290104q11a767b6qcc1acc4c2d1feba6@mail.gmail.com> (raw)
In-Reply-To: <20090629072047.GB20225@elte.hu>
On Mon, Jun 29, 2009 at 3:20 PM, Ingo Molnar<mingo@elte.hu> wrote:
>
> * Luming Yu <luming.yu@gmail.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?
It is hang caused by kernel code for work around lapic-timer-stop issue.
With HZ=1000, and a lot of cpus (eg. 64 logical cpus), cpu 0 will be
busy working on send TIMER IPI instead of making progress in boot
(right after deep-C-state has been used).
>
> Ingo
>
next prev parent reply other threads:[~2009-06-29 8:04 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-06-29 6:47 Luming Yu
2009-06-29 7:20 ` Ingo Molnar
2009-06-29 8:04 ` Luming Yu [this message]
2009-06-29 8:16 ` Ingo Molnar
2009-06-29 8:21 ` Luming Yu
2009-06-29 8:30 ` Ingo Molnar
2009-06-29 8:43 ` Luming Yu
2009-06-29 9:15 ` Ingo Molnar
2009-06-29 14:01 ` Arjan van de Ven
2009-06-29 20:34 ` Pallipadi, Venkatesh
2009-06-30 7:01 ` Luming Yu
2009-07-03 0:23 ` Pallipadi, Venkatesh
2009-07-03 2:04 ` Luming Yu
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