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Re: [PATCH v4 2/2] trace: Example of non-tracing recorder use

From: Stefan Hajnoczi
Subject: Re: [PATCH v4 2/2] trace: Example of non-tracing recorder use
Date: Mon, 3 Aug 2020 11:44:32 +0100

On Thu, Jul 23, 2020 at 03:29:03PM +0200, Christophe de Dinechin wrote:
> This patch is a simple example showing how the recorder can be used to
> have one "topic" covering multiple entries. Here, the topic is "lock",
> the idea being to have the latest lock changes for instance in case of
> a crash or hang.
> Here are a few use cases:
> * Tracing  lock updates:
>     RECORDER_TRACES=lock qemu
> * Showing lock changes prior to a hang
>     RECORDER_TRACES=lock qemu &
>     # Wait until hang
>     killall -USR2 qemu  # This will trigger a dump
> * Graphic visualization of lock states:
>     RECORDER_TRACES="lock=state,id" qemu &
>     recorder_scope state
>     # Hit the 't' key to toggle timing display
>     # Hit the 'c' key to dump the screen data as CSV
>     cat recorder_scope_data-1.csv

Dan raised a good point regarding integrating recorder functionality
behind the tracetool interface.

On the other hand, I would like to see where this goes so that we have
enough experience to design the tracetool interface, if necessary.

Therefore I am for merging this as-is and taking action when it's clear
that duplication is taking place.


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