lkml.org 
[lkml]   [2014]   [Oct]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Progress on system crash traces with LTTng using DAX and pmem
----- Original Message -----
> From: "Kirill A. Shutemov" <kirill@shutemov.name>
> To: "Mathieu Desnoyers" <mathieu.desnoyers@efficios.com>
> Cc: "Matthew Wilcox" <willy@linux.intel.com>, "Ross Zwisler" <ross.zwisler@linux.intel.com>, "lttng-dev"
> <lttng-dev@lists.lttng.org>, 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


\
 
 \ /
  Last update: 2014-10-30 16:21    [W:0.123 / U:0.064 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site