Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752934AbZF2IEs (ORCPT ); Mon, 29 Jun 2009 04:04:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751489AbZF2IEd (ORCPT ); Mon, 29 Jun 2009 04:04:33 -0400 Received: from mail-px0-f190.google.com ([209.85.216.190]:55350 "EHLO mail-px0-f190.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751073AbZF2IEc convert rfc822-to-8bit (ORCPT ); Mon, 29 Jun 2009 04:04:32 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=vIx07IS13TpUBjort78gpjRBR6Bf/Deqtj0hOpJdiOa6satH60hPD2Ct1nUmhqfb4w 2sdTLN4iPnWcFHW2DVNKhlvTsAekqqOq1tp4RXupleWiqMnqpjxqROrPXx/UUJ2VFy2j ZG1xu+wwzfLcSZkBwsNaDLTrLaKJv0OGSq/Wg= MIME-Version: 1.0 In-Reply-To: <20090629072047.GB20225@elte.hu> References: <3877989d0906282347i311eb14bp80a7c80878219c31@mail.gmail.com> <20090629072047.GB20225@elte.hu> Date: Mon, 29 Jun 2009 16:04:35 +0800 Message-ID: <3877989d0906290104q11a767b6qcc1acc4c2d1feba6@mail.gmail.com> Subject: Re: [RFC patch] Use IPI_shortcut for lapic timer broadcast From: Luming Yu To: Ingo Molnar Cc: LKML , suresh.b.siddha@intel.com, venkatesh.pallipadi@intel.com, Thomas Gleixner , "H. Peter Anvin" Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1027 Lines: 31 On Mon, Jun 29, 2009 at 3:20 PM, Ingo Molnar wrote: > > * Luming Yu 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 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/