Back to the future with C++ and Seastar
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Seastar is an open source framework that provides highly scalable and asynchronous distributed applications. It uses a shared-nothing architecture with no locks or threads to achieve linear scaling across cores. Applications built on Seastar can handle millions of connections and I/O operations in parallel. It uses an asynchronous programming model based on promises and futures with zero-copy networking and disk I/O for high performance.
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Back to the future with C++ and Seastar
- 1. Cloudius Systems presents: Seastar Avi Kivity, April 13 2015
- 2. ● New tech, runs on physical machines, VMs,Linux/OSv ● Multi-million IOPS, fully scalable ● Perfect building block for database/filesystem/cache ● Share-nothing, fully asynchronous model ● Open Source SeaStar Technology
- 4. SeaStar Before: Thread model After: SeaStar shards
- 5. Problem with today’s programing model + Single core performance (frequency, IPC) no longer growing + #core grows but it’s hard to utilize. Apps don’t scale + Locks have costs even w/o contention + Data is allocated on one core, copied and used on others + Software can’t keep up with the recent hardware (SSD, line rate for 10Gbps, NUMA, etc) Kernel Application TCP/IPScheduler queuequeuequeuequeuequeue threads NIC Queues Kernel Traditional stack Memory
- 6. SeaStar Framework Linear scaling by #core + Each engine is executed by each core + Shared-nothing per-core design + Fits existing shared-nothing distributed applications model + Full kernel bypass, supports zero-copy + No threads, no context switch and no locks + Instead, asynchronous lambda invocation Application TCP/IP Task Scheduler queuequeuequeuequeuequeuesmp queue NIC Queue DPDK Kernel (isn’t involved) Userspace Application TCP/IP Task Scheduler queuequeuequeuequeuequeuesmp queue NIC Queue DPDK Kernel (isn’t involved) Userspace Application TCP/IP Task Scheduler queuequeuequeuequeuequeuesmp queue NIC Queue DPDK Kernel (isn’t involved) Userspace Application TCP/IP Task Scheduler queuequeuequeuequeuequeuesmp queue NIC Queue DPDK Kernel (isn’t involved) Userspace
- 7. Kernel SeaStar Framework Comparison Application TCP/IPScheduler queuequeuequeuequeuequeue threads NIC Queues Kernel Traditional stack SeaStar’s sharded stack Memory Lock contention Cache contention NUMA unfriendly Application TCP/IP Task Scheduler queuequeuequeuequeuequeuesmp queue NIC Queue DPDK Kernel (isn’t involved) Userspace Application TCP/IP Task Scheduler queuequeuequeuequeuequeuesmp queue NIC Queue DPDK Kernel (isn’t involved) Userspace Application TCP/IP Task Scheduler queuequeuequeuequeuequeuesmp queue NIC Queue DPDK Kernel (isn’t involved) Userspace Application TCP/IP Task Scheduler queuequeuequeuequeuequeuesmp queue NIC Queue DPDK Kernel (isn’t involved) Userspace No contention Linear scaling NUMA friendly
- 8. SeaStar handles 1,000,000s connections in parallel! Traditional stack SeaStar’s sharded stack Promise Task Promise Task Promise Task Promise Task CPU Promise Task Promise Task Promise Task Promise Task CPU Promise Task Promise Task Promise Task Promise Task CPU Promise Task Promise Task Promise Task Promise Task CPU Promise Task Promise Task Promise Task Promise Task CPU Promise is a pointer to eventually computed value Task is a pointer to a lambda function Scheduler CPU Scheduler CPU Scheduler CPU Scheduler CPU Scheduler CPU Thread Stack Thread Stack Thread Stack Thread Stack Thread Stack Thread Stack Thread Stack Thread Stack Thread is a function pointer Stack is a byte array from 64k to megabytes Context switch cost is high. Large stacks pollutes the caches No sharing, millions of parallel events
- 9. SeaStar current performance Stock TCP stack SeaStar’s native TCP stack
- 10. Basic model ■ Futures ■ Promises ■ Continuations
- 11. F-P-C defined: Future A future is a result of a computation that may not be available yet. ■ Data buffer from the network ■ Timer expiration ■ Completion of a disk write ■ Result computation that requires the values from one or more other futures.
- 12. F-P-C defined: Promise A promise is an object or function that provides you with a future, with the expectation that it will fulfil the future.
- 13. Basic future/promise future<int> get(); // promises an int will be produced eventually future<> put(int) // promises to store an int void f() { get().then([] (int value) { put(value + 1).then([] { std::cout << "value stored successfullyn"; }); }); }
- 14. Chaining future<int> get(); // promises an int will be produced eventually future<> put(int) // promises to store an int void f() { get().then([] (int value) { return put(value + 1); }).then([] { std::cout << "value stored successfullyn"; }); }
- 15. Zero copy friendly future<temporary_buffer> connected_socket::read(size_t n); ■ temporary_buffer points at driver-provided pages if possible ■ discarded after use
- 16. Zero copy friendly (2) future<size_t> connected_socket::write(temporary_buffer); ■ Future becomes ready when TCP window allows sending more data (usually immediately) ■ temporary_buffer discarded after data is ACKed ■ can call delete[] or decrement a reference count
- 17. Dual Networking Stack Networking API Seastar (native) Stack POSIX (hosted) stack Linux kernel (sockets) User-space TCP/IP Interface layer DPDK Virtio Xen igb ixgb
- 18. Disk I/O ■ Zero copy using Linux AIO and O_DIRECT ■ Some operations using worker threads (open() etc.) ■ Plans for direct NVMe support
- 19. Rich APIs ● HTTP Server ● HTTP Client ● RPC client/server ● map_reduce ● parallel_for_each ● distributed<> ● when_all() ● timers
- 20. More info ■ http://github.com/cloudius-systems/seastar ■ http://seastar-project.com