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Date:   Thu, 03 Sep 2020 11:06:47 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
To:     Joel Fernandes <joel@joelfernandes.org>
Cc:     Nachammai Karuppiah <nachukannan@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Rob Herring <robh+dt@kernel.org>,
        Frank Rowand <frowand.list@gmail.com>,
        Kees Cook <keescook@chromium.org>,
        Anton Vorontsov <anton@enomsg.org>,
        Colin Cross <ccross@android.com>,
        Tony Luck <tony.luck@intel.com>,
        LKML <linux-kernel@vger.kernel.org>, computersforpeace@gmail.com
Subject: Re: [RFC PATCH 0/7] Trace events to pstore
In-Reply-To: <CAEXW_YSt49yGH+Wc63zfm4i7n1M_YxETbAA8nxmfDH1B3WFQXg@mail.gmail.com>
References: <cover.1599072725.git.nachukannan@gmail.com>
 <CAEXW_YSt49yGH+Wc63zfm4i7n1M_YxETbAA8nxmfDH1B3WFQXg@mail.gmail.com>
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On 2020-09-03 03:17, Joel Fernandes wrote:
> On Wed, Sep 2, 2020 at 4:01 PM Nachammai Karuppiah
> <nachukannan@gmail.com> wrote:
>> 
>> Hi,
>> 
>> This patch series adds support to store trace events in pstore.
>> 
>> Storing trace entries in persistent RAM would help in understanding 
>> what
>> happened just before the system went down. The trace events that led 
>> to the
>> crash can be retrieved from the pstore after a warm reboot. This will 
>> help
>> debug what happened before machine’s last breath. This has to be done 
>> in a
>> scalable way so that tracing a live system does not impact the 
>> performance
>> of the system.
> 
> Just to add, Nachammai was my intern in the recent outreachy program
> and we designed together a way for trace events to be written to
> pstore backed memory directory instead of regular memory. The basic
> idea is to allocate frace's ring buffer on pstore memory and have it
> right there. Then recover it on reboot. Nachammai wrote the code with
> some guidance :) . I talked to Steve as well in the past about the
> basic of idea of this. Steve is on vacation this week though.
> 
> This is similar to what +Sai Prakash Ranjan was trying to do sometime
> ago: https://lkml.org/lkml/2018/9/8/221 . But that approach involved
> higher overhead due to synchronization of writing to the otherwise
> lockless ring buffer.
> 
> +Brian Norris has also expressed interest for this feature.
> 

Great work Nachammai and Joel, I have few boards with warm reboot 
support and will test
this series in coming days.

Thanks,
Sai

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