Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760713AbaJ3PLo (ORCPT ); Thu, 30 Oct 2014 11:11:44 -0400 Received: from mail.efficios.com ([78.47.125.74]:37761 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760395AbaJ3PLm (ORCPT ); Thu, 30 Oct 2014 11:11:42 -0400 Date: Thu, 30 Oct 2014 15:11:36 +0000 (UTC) From: Mathieu Desnoyers To: "Kirill A. Shutemov" Cc: Matthew Wilcox , Ross Zwisler , lttng-dev , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andi Kleen Message-ID: <864133911.4806.1414681896478.JavaMail.zimbra@efficios.com> In-Reply-To: <20141028105458.GA9768@node.dhcp.inet.fi> References: <1254279794.1957.1414240389301.JavaMail.zimbra@efficios.com> <465653369.1985.1414241485934.JavaMail.zimbra@efficios.com> <20141028105458.GA9768@node.dhcp.inet.fi> Subject: Re: Progress on system crash traces with LTTng using DAX and pmem MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [173.246.22.116] X-Mailer: Zimbra 8.0.7_GA_6021 (ZimbraWebClient - FF32 (Linux)/8.0.7_GA_6021) Thread-Topic: Progress on system crash traces with LTTng using DAX and pmem Thread-Index: nJK2oOzjzWDWdtzR4jvZJFWqNfbeOA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- Original Message ----- > From: "Kirill A. Shutemov" > To: "Mathieu Desnoyers" > Cc: "Matthew Wilcox" , "Ross Zwisler" , "lttng-dev" > , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org > Sent: Tuesday, October 28, 2014 6:54:58 AM > Subject: Re: Progress on system crash traces with LTTng using DAX and pmem > > On Sat, Oct 25, 2014 at 12:51:25PM +0000, Mathieu Desnoyers wrote: > > FYI, the main reason why my customer wants to go with a > > "trace into memory that survives soft reboot" approach > > rather than to use things like kexec/kdump is that they > > care about the amount of time it takes to reboot their > > machines. They want a solution where they can extract the > > detailed crash data after reboot, after the machine is > > back online, rather than requiring a few minutes of offline > > time to extract the crash details. > > IIRC, on x86 there's no guarantee that your memory content will be > preserved over reboot. BIOS is free to mess with it. Hi Kirill, This is a good point, There are a few more aspects to consider here: - Other architectures appear to have different guarantees, for instance ARM which, AFAIK, does not reset memory on soft reboot (well at least for my customer's boards). So I guess if x86 wants to be competitive, it would be good for them to offer a similar feature, - Already having a subset of machines supporting this is useful, e.g. storing trace buffers and recovering them after a crash, - Since we are in a world of dynamically upgradable BIOS, perhaps if we can show that there is value in having a BIOS option to specify a memory range that should not be reset on soft reboot, BIOS vendors might be inclined to include an option for it, - Perhaps UEFI BIOS already have some way of specifying that a memory range should not be reset on soft reboot ? Thoughts ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com -- 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/