Difference between revisions of "Comparison to other CR projects"

Revision as of 13:58, 11 July 2013

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

DMTCP

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

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.

CRIU, DMTCP, BLCR

“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
Arch	x86_64, ARM	x86, x86_64, ARM	x86, x86_64, PPC/PPC64, ARM
OS	Linux	Linux	Linux
Need in modified kernel	Yes, but only for some extra features. All unnecessary features are already in new kernel versions	No	No, just need to load module. May be problems with installation on new kernels
App need to pre-load special libraries	No	Yes	Yes
Requires root privileges	Yes, due to restrictions from some kernel APIs it uses	No	No
Need to modify programs to C/R	No	No	Yes. There are some difficulties with statically linked applications, and with LinuxThreads (it does not support them at all)
Need to prepare tasks	No	Yes. It preloadsthe DMTCP library. That library runs before the routinemain(). It creates a second thread. Thecheckpoint thread then creates a socket to the DMTCP coordinator andregisters itself. The checkpoint thread also creates a signal handler.	Yes. CR shall notify processes when a checkpoint is to occur (before the kernel takes a checkpoint) to allow the processes to prepare itself accordingly.
Does it change behavior of the c/r-ed programs?	No	Yes, because of wrappers on system calls	Yes, because of wrappers on system calls
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
Containers	Yes, LXC and OpenVZ containers	No. It doesn't support namespaces, so it probably can’t dump containers	Looks like no
Parallel/distributed computations libraries	No (in plans)	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
C/R gdb with debugging app	No, because they are using the same interface	Yes	No
X-Windows apps (KDE, GNOME, etc)	Yes, by using vnc	Yes, by using vnc	Looks like no
Solutions for invocation in the custom software	No, only fork + daemonize + exec	Yes. Plugins and API	Not yet

Unix sockets	Yes	Yes	No
UDP sockets	Yes, both ipv4 and ipv6	Not yet. Developers of dmtcp had no request for this	Not yet
TCP sockets	Yes	Yes	Not yet
Established tcp connection	Yes	No, but you can write a simple DMTCP plugin that tells DMTCP how you want to reconnect on restart	No
Infiniband	No	Not yet, developing is on the half-way	No
Multithread support	Yes	Yes	Yes
Multiprocess	Yes	Yes	Yes
Process groups and sessions	Yes	Yes	Not yet
Zombies	Yes	No	No
Namespaces	Yes	No	No
Ptraced programs	No	Yes	No
System V IPC	Yes	Yes	No
Memory mappings	Yes, all kinds	Yes	Yes, partially
Pipes	Yes	Yes	Not yet
Terminals	Yes, but only Unix98 PTYs	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
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
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 suppord shared mmap regions
Block devices	No	Looks like yes	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
Capture the contents of open files	Yes, if file is unlinked	Looks like no	Not yet

Sources

DMTCP:

BLCR:

External links

How does DMTCP work?