From: "Pavel Dovgaluk" <Pavel.Dovgaluk@ispras.ru>
References: <20141126103841.7772.11864.stgit@PASHA-ISP>
In-Reply-To: <20141126103841.7772.11864.stgit@PASHA-ISP>
Date: Wed, 26 Nov 2014 13:47:48 +0300
Message-ID: <000901d00966$6c499460$44dcbd20$@Dovgaluk@ispras.ru>
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Subject: Re: [Qemu-devel] [RFC PATCH v5 00/31] Deterministic replay and
	reverse execution
To: 'Pavel Dovgalyuk' <Pavel.Dovgaluk@ispras.ru>, qemu-devel@nongnu.org
Cc: peter.maydell@linaro.org, peter.crosthwaite@xilinx.com, alex.bennee@linaro.org, mark.burton@greensocs.com, real@ispras.ru, batuzovk@ispras.ru, maria.klimushenkova@ispras.ru, pbonzini@redhat.com, afaerber@suse.de, fred.konrad@greensocs.com

That covermail was wrong. Here is the correct one:


This set of patches is related to the reverse execution and =
deterministic=20
replay of qemu execution  This implementation of deterministic replay =
can=20
be used for deterministic debugging of guest code through gdb remote
interface.

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=20
used for replaying the execution anywhere and for unlimited number of =
times.=20
It also supports checkpointing for faster rewinding during reverse =
debugging.=20
Execution replaying reads the log and replays all non-deterministic =
events=20
including external input, hardware clocks, and interrupts.

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=20
   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:
 * First, record the execution, by adding the following string to the =
command line:
   '-record fname=3Dreplay.bin -icount 7 -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: '-replay fname=3Dreplay.bin -icount 7 -net none'
 * '-net none' option should also be specified if network replay patches
   are not applied.

Paper with short description of deterministic replay implementation:
http://www.computer.org/csdl/proceedings/csmr/2012/4666/00/4666a553-abs.h=
tml

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 bottom halves execution
 * synchronization of the threads from thread pool
 * recording/replaying user input (mouse and keyboard)
 * adding internal events for cpu and io synchronization

v5 changes:
 * Minor changes.
 * Used fixed-width integer types for read/write functions (as suggested =
by Alex Bennee)
 * Moved savevm-related code out of the core.
 * Added new traced clock for deterministic virtual clock warping (as =
suggested by Paolo Bonzini)
 * Fixed exception_index reset for user mode (as suggested by Paolo =
Bonzini)
 * Adopted Paolo's icount patches
 * Fixed hardware interrupts replaying

v4 changes:
 * Updated block drivers to support new bdrv_open interface.
 * Moved migration patches into separate series (as suggested by Paolo =
Bonzini)
 * Fixed a bug in replay_break operation.
 * Fixed rtl8139 migration for replay.
 * Fixed 'period' parameter processing for record mode.
 * Fixed bug in 'reverse-stepi' implementation.
 * Fixed replay without making any snapshots (even the starting one).
 * Moved core replay patches into the separate series.
 * Fixed reverse step and reverse continue support.
 * Fixed several bugs in icount subsystem.
 * Reusing native qemu icount for replay instructions counting.
 * Separated core patches into their own series.

v3 changes:
 * Fixed bug with replay of the aio write operations.
 * Added virtual clock based on replay icount.
 * Removed duplicated saving of interrupt_request CPU field.
 * Fixed some coding style issues.
 * Renamed QMP commands for controlling reverse execution (as suggested =
by Eric Blake)
 * Replay mode and submode implemented as QAPI enumerations (as =
suggested by Eric Blake)
 * Added description and example for replay-info command (as suggested =
by Eric Blake)
 * Added information about the current breakpoint to the output of =
replay-info (as suggested by Eric Blake)
 * Updated version id for HPET vmstate (as suggested by Paolo Bonzini)
 * Removed static fields from parallel vmstate (as suggested by Paolo =
Bonzini)
 * New vmstate fields for mc146818rtc, pckbd, kvmapic, serial, fdc, =
rtl8139 moved to subsection (as suggested by Paolo Bonzini)
 * Disabled textmode cursor blinking, when virtual machine is stopped =
(as suggested by Paolo Bonzini)
 * Extracted saving of exception_index to separate patch (as suggested =
by Paolo Bonzini)

v2 changes:
 * Patches are split to be reviewable and bisectable (as suggested by =
Kirill Batuzov)
 * Added QMP versions of replay commands (as suggested by Eric Blake)
 * Removed some optional features of replay to make patches cleaner
 * Minor changes and code cleanup were made