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Re: [Qemu-devel] [RFC PATCH v13 00/21] Deterministic replay core

From: Pavel Dovgaluk
Subject: Re: [Qemu-devel] [RFC PATCH v13 00/21] Deterministic replay core
Date: Tue, 19 May 2015 10:44:51 +0300


> -----Original Message-----
> From: Pavel Dovgalyuk [mailto:address@hidden
> Sent: Wednesday, May 06, 2015 5:03 PM
> To: address@hidden
> Cc: address@hidden; address@hidden; address@hidden;
> address@hidden; address@hidden; address@hidden; address@hidden;
> address@hidden; address@hidden; address@hidden;
> address@hidden
> Subject: [RFC PATCH v13 00/21] Deterministic replay core
> This set of patches is related to the reverse execution and deterministic
> replay of qemu execution. This implementation of deterministic replay can
> be used for deterministic debugging of guest code through gdb remote
> interface.
> Core set of patches does not include support for reverse debugging commands
> of gdb, block devices' operations, USB replay support.
> These patches include only core function of the replay,
> excluding the support for replaying serial, audio, network, and USB devices'
> operations. Reverse debugging and monitor commands were also excluded to
> be submitted later as separate patches.
> Execution recording writes non-deterministic events log, which can be later
> used for replaying the execution anywhere and for unlimited number of times.
> It also supports checkpointing for faster rewinding during reverse debugging.
> Execution replaying reads the log and replays all non-deterministic events
> including external input, hardware clocks, and interrupts.
> Full version of deterministic replay has the following features:
>  * Deterministically replays whole system execution and all contents of the 
> memory,
>    state of the hadrware devices, clocks, and screen of the VM.
>  * Writes execution log into the file for latter replaying for multiple times
>    on different machines.
>  * Supports i386, x86_64, and ARM hardware platforms.
>  * Performs deterministic replay of all operations with keyboard and mouse
>    input devices.
>  * Supports auto-checkpointing for convenient reverse debugging.
> Usage of the record/replay core:
>  * First, record the execution, by adding the following string to the command 
> line:
>    '-icount shift=7,rr=record,rrfile=replay.bin -net none'.
>    Block devices' images are not actually changed in the recording mode,
>    because all of the changes are written to the temporary overlay file.
>  * Then you can replay it for the multiple times by using another command
>    line option: '-icount shift=7,rr=replay,rrfile=replay.bin -net none'
>  * '-net none' option should also be specified if network replay patches
>    are not applied.
>  * Do not add any disk images to VM, because they are not supported by
>    the core patches.
> Paper with short description of deterministic replay implementation:
> http://www.computer.org/csdl/proceedings/csmr/2012/4666/00/4666a553-abs.html
> Modifications of qemu include:
>  * wrappers for clock and time functions to save their return values in the 
> log
>  * saving different asynchronous events (e.g. system shutdown) into the log
>  * synchronization of the threads from thread pool
>  * recording/replaying user input (mouse and keyboard)
>  * adding internal events for cpu and io synchronization
> v13 changes:
>  * Introduced "ptimer trigger" event (as suggested by Paolo Bonzini)

Can anyone review the remaining patches?

Pavel Dovgalyuk

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