linux-kernel - Re: Progress on system crash traces with LTTng using DAX and pmem

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Date:	Sat, 13 Dec 2014 11:48:27 +0000
From:	Matt Fleming <matt@...sole-pimps.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	"Kirill A. Shutemov" <kirill@...temov.name>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	lttng-dev <lttng-dev@...ts.lttng.org>,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>,
	linux-efi@...r.kernel.org, Tony Luck <tony.luck@...il.com>
Subject: Re: Progress on system crash traces with LTTng using DAX and pmem

On Thu, 30 Oct, at 03:11:36PM, Mathieu Desnoyers wrote:
> 
> 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 ?

We've achieved this in the past using UEFI capsules with the
EFI_CAPSULE_PERSIST_ACROSS_RESET header flag.

Unfortunately, runtime capsule support is pretty spotty, so it's not a
general solution right now.

-- 
Matt Fleming, Intel Open Source Technology Center
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