Difference between revisions of "Comparison to other CR projects"

Latest revision as of 19:20, 9 December 2015

This pages tries to explain differences between CRIU and other C/R solutions.

DMTCP[edit]

DMTCP implements checkpoint/restore of a process on a library level. This means, that if you want to C/R some application you should launch one with DMTCP library (dynamically) linked from the very beginning. When launched like this, the DMTCP library intercepts a certain amount of library calls from the application, builds a shadow data-base of information about process' internals and then forwards the request down to glibc/kernel. The information gathered is to be used to create an image of the application. With this approach, one can only dump applications known to run successfully with the DMTCP libraries, but the latter doesn't provide proxies for all kernel APIs (for example, inotify() is known to be unsupported). Another implication of this approach is potential performance issues that arise due to proxying of requests.

Restoration of process set is also tricky, as it frequently requires restoring an object with the predefined ID and kernel is known to provide no APIs for several of them. For example, kernel cannot fork a process with the desired PID. To address that, DMTCP fools a process by intercepting the getpid() library call and providing fake PID value to the application. Such behavior is very dangerous, as application might see wrong files in the /proc filesystem if it will try to access one via its PID.

CRIU, on the other hand, doesn't require any libraries to be pre-loaded. It will checkpoint and restore any arbitrary application, as long as kernel provides all needed facilities. Kernel support for some of CRIU features were added recently, essentially meaning that a recent kernel version might be required.

BLCR[edit]

Berkeley Lab Checkpoint/Restart (BLCR) is a part of the Scalable Systems Software Suite , developed by the Future Technologies Group at Lawrence Berkeley National Lab under SciDAC funding from the United States Department of Energy. It is an Open Source, system-level checkpointer designed with High Performance Computing (HPC) applications in mind: in particular CPU and memory intensive batch-scheduled MPI jobs. BLCR is implemented as a GPL-licensed loadable kernel module for Linux 2.4.x and 2.6.x kernels on the x86, x86_64, PPC/PPC64, ARM architectures, and a small LGPL-licensed library.

PinLIT / PinPlay[edit]

PinLIT (Pin-Long Instruction Trace) is a checkpointing tool built on top of Intel's proprietary PIN binary instrumentation tool described on page 48 of Cristiano Pereira's PhD thesis. It records the processor's (big) architectural register state and all pages of memory that contain application and shared library code, optimizing size by only storing memory used during a desired interval.

PinPlay or the Program Record/Replay Toolkit appears to be the successor of or new name for PinLIT.

Both tools appear primarily focused on reducing benchmark runtime on slow computer architecture simulators, leveraging sampling algorithms such as SimPoint.

OpenVZ (in-kernel)[edit]

Legacy OpenVZ (RHEL4, RHEL5, RHEL6 based kernels) has in-kernel checkpoint/restore, sources can be found in kernel/cpt/.

CKPT (in-kernel)[edit]

(In-kernel) Linux Checkpoint/Restart was a project from around 2008 to around 2010 to implement checkpoint/restart of Linux processes.

CRIU, DMTCP, BLCR, OpenVZ comparison table[edit]

“looks\seems like yes/no” - i found only unproved message(s) saying “yes”/“no”

“not yet” - it is officially planned or i found no reasons, why it can’t be done.

	CRIU	DMTCP	BLCR	OpenVZ
Arch	x86_64, ARM, AArch64, PPC64le	x86, x86_64, ARM	x86, x86_64, PPC/PPC64, ARM	x86, x86_64
OS	Linux	Linux	Linux	Linux
Uses standard kernel?	Yes, provided it's 3.11 or later	Yes	Yes, just needs to load module	No. OpenVZ kernel is required
Can be used without preloading special libraries before app start?	Yes	No	No	Yes
Can be used as non-root user?	Yes, but user can only manipulate tasks belonging to him	Yes	Yes	No
Can run unmodified programs?	Yes	Yes	No. Statically linked and/or threaded apps are unsupported.	Yes
Can run unprepared tasks?	Yes	No. It preloads the DMTCP library. That library runs before the routine main(). It creates a second thread. The checkpoint thread then creates a socket to the DMTCP coordinator and registers itself. The checkpoint thread also creates a signal handler.	No. CR shall notify processes when a checkpoint is to occur (before the kernel takes a checkpoint) to allow the processes to prepare itself accordingly.	Yes
Retains behavior of the c/r-ed programs?	Yes (but see What can change after C/R)	No, because of wrappers on system calls	No, because of wrappers on system calls	Yes
Live migration	Yes, even if kernel, libs, etc are newer. Can use memory changes tracking to decrease freeze time	Yes, if both kernels are recent	Yes, but if all components are the same. Even if prelinked addresses are different, it will not restore, but it can save the whole used libs and localization files to restore program on the different machine	Yes
Containers	Yes, LXC and OpenVZ containers	No. It doesn't support namespaces, so it probably can’t dump containers	Looks like no	Yes
Parallel/distributed computations libraries	No (planned)	Yes. OpenMPI, MPICH2, OpenMP, Cilk are alredy supported and Infiniband is in progress	Yes. Cray MPI, Intel MPI, LAM/MPI, MPICH-V, MPICH2, MVAPICH, Open MPI, SGI MPT	Yes
Possible to C/R of gdb with debugged app?	No, because they are using the same interface	Yes	No	Yes
X Window apps (KDE, GNOME, etc)	Yes, via VNC	Yes, via VNC	Looks like no	Yes, via VNC
Solutions for invocation in the custom software	Yes, RPC and C API	Yes, plugins and API	Not yet	Yes, via ioctl calls

Unix sockets	Yes	Yes	No	Yes
UDP sockets	Yes, both ipv4 and ipv6	Not yet. Developers of dmtcp had no request for this	Not yet	Yes
TCP sockets	Yes	Yes	Not yet	Yes
Established TCP connection	Yes	No, but you can write a simple DMTCP plugin that tells DMTCP how you want to reconnect on restart	No	Yes
Infiniband	No	Not yet, developing is on the half-way	No	No
Multithread support	Yes	Yes	Yes	Yes
Multiprocess	Yes	Yes	Yes	Yes
Process groups and sessions	Yes	Yes	Not yet	Yes
Zombies	Yes	No	No	Yes
Namespaces	Yes	No	No	Yes
Ptraced programs	No	Yes	No	Yes
System V IPC	Yes	Yes	No	Yes
Memory mappings	Yes, all kinds	Yes	Partial	Yes
Pipes	Yes	Yes	Not yet	Yes
Terminals	Yes, but only Unix98 PTYs	Yes	Yes	Yes
Non-POSIX files (inotify, signalfd, eventfd, etc)	Yes, inotify, fanotify, epoll, signalfd, eventfd	Yes, epoll, eventfd, signalfd are already supported and inotify will be supported in future	Looks like no	Yes
Timers	Yes	No. Any counter or timer active since the beginning of a process will consider the restarted process to be a new process.	Yes	Yes
Shared resources (files, mm, etc.)	Yes. SysVIPC, files, fd table and memory	Yes. System V shared memory(shmget, etc.), mmap-based shared memory, shared sockets, pipes, file descriptors	No, but it is planned to support shared mmap regions	Yes
Block devices	No	Looks like yes	No	No
Character devices	Yes, only /dev/null, /dev/zero, etc. are supported	Yes, looks like null and zero are supported	Yes, /dev/null and /dev/zero	Yes
Capture the contents of open files	Yes, if file is unlinked	Looks like no	Not yet	Yes

Sources[edit]

DMTCP:

BLCR:

External links[edit]

How does DMTCP work?

@@ Line 22: / Line 22: @@
 Both tools appear primarily focused on reducing benchmark runtime on slow computer architecture simulators, leveraging sampling algorithms such as SimPoint.
+== OpenVZ (in-kernel) ==
+Legacy OpenVZ (RHEL4, RHEL5, RHEL6 based kernels) has in-kernel checkpoint/restore, sources can be found in kernel/cpt/.
+== CKPT (in-kernel) ==
+(In-kernel) [https://ckpt.wiki.kernel.org/index.php/Main_Page Linux Checkpoint/Restart] was a project from around 2008 to around 2010 to implement checkpoint/restart of Linux processes.
 == CRIU, DMTCP, BLCR, OpenVZ comparison table ==
@@ Line 40: / Line 48: @@
 |-
 | Arch
-| x86_64, ARM
+| x86_64, ARM, AArch64, PPC64le
 | x86, x86_64, ARM
 | x86, x86_64, PPC/PPC64, ARM
@@ Line 89: / Line 97: @@
 |-
 | Retains behavior of the c/r-ed programs?
-| {{Yes}}
+| {{Yes}} (but see [[What can change after C/R]])
 | {{No}}, because of wrappers on system calls
 | {{No}}, because of wrappers on system calls
@@ Line 96: / Line 104: @@
 |-
 | Live migration
-| {{Yes}}, even if kernel, libs, etc are newer. Can use Memory Changes Tracking to decrease freeze time
+| {{Yes}}, even if kernel, libs, etc are newer. Can use [[memory changes tracking]] to decrease freeze time
 | {{Yes}}, if both kernels are recent
 | {{Yes}}, but if all components are the same. Even if prelinked addresses are different, it will not restore, but it can save the whole used libs and localization files to restore program on the different machine