======= crimson ======= Crimson is the code name of ``crimson-osd``, which is the next generation ``ceph-osd``. It improves performance when using fast network and storage devices, employing state-of-the-art technologies including DPDK and SPDK. BlueStore continues to support HDDs and slower SSDs. Crimson aims to be backward compatible with the classic ``ceph-osd``. .. highlight:: console Building Crimson ================ Crimson is not enabled by default. Enable it at build time by running:: $ WITH_SEASTAR=true ./install-deps.sh $ mkdir build && cd build $ cmake -DWITH_SEASTAR=ON .. Please note, `ASan`_ is enabled by default if Crimson is built from a source cloned using ``git``. .. _ASan: https://github.com/google/sanitizers/wiki/AddressSanitizer Testing crimson with cephadm =============================== The Ceph CI/CD pipeline builds containers with ``crimson-osd`` subsitituted for ``ceph-osd``. Once a branch at commit has been built and is available in ``shaman``, you can deploy it using the cephadm instructions outlined in :ref:`cephadm` with the following adaptations. First, while performing the initial bootstrap, use the ``--image`` flag to use a Crimson build: .. prompt:: bash # cephadm --image quay.ceph.io/ceph-ci/ceph:-crimson --allow-mismatched-release bootstrap ... You'll likely need to supply the ``--allow-mismatched-release`` flag to use a non-release branch. Additionally, prior to deploying OSDs, you'll need enable Crimson to direct the default pools to be created as Crimson pools. From the cephadm shell run: .. prompt:: bash # ceph config set global 'enable_experimental_unrecoverable_data_corrupting_features' crimson ceph osd set-allow-crimson --yes-i-really-mean-it ceph config set mon osd_pool_default_crimson true The first command enables the ``crimson`` experimental feature. Crimson is highly experimental, and malfunctions including crashes and data loss are to be expected. The second enables the ``allow_crimson`` OSDMap flag. The monitor will not allow ``crimson-osd`` to boot without that flag. The last causes pools to be created by default with the ``crimson`` flag. Crimson pools are restricted to operations supported by Crimson. ``Crimson-osd`` won't instantiate PGs from non-Crimson pools. Running Crimson =============== As you might expect, Crimson does not yet have as extensive a feature set as does ``ceph-osd``. object store backend -------------------- At the moment, ``crimson-osd`` offers both native and alienized object store backends. The native object store backends perform IO using the SeaStar reactor. They are: .. describe:: cyanstore CyanStore is modeled after memstore in the classic OSD. .. describe:: seastore Seastore is still under active development. The alienized object store backends are backed by a thread pool, which is a proxy of the alienstore adaptor running in Seastar. The proxy issues requests to object stores running in alien threads, i.e., worker threads not managed by the Seastar framework. They are: .. describe:: memstore The memory backed object store .. describe:: bluestore The object store used by the classic ``ceph-osd`` daemonize --------- Unlike ``ceph-osd``, ``crimson-osd`` does not daemonize itself even if the ``daemonize`` option is enabled. In order to read this option, ``crimson-osd`` needs to ready its config sharded service, but this sharded service lives in the Seastar reactor. If we fork a child process and exit the parent after starting the Seastar engine, that will leave us with a single thread which is a replica of the thread that called `fork()`_. Tackling this problem in Crimson would unnecessarily complicate the code. Since supported GNU/Linux distributions use ``systemd``, which is able to daemonize the application, there is no need to daemonize ourselves. Those using sysvinit can use ``start-stop-daemon`` to daemonize ``crimson-osd``. If this is does not work out, a helper utility may be devised. .. _fork(): http://pubs.opengroup.org/onlinepubs/9699919799/functions/fork.html logging ------- ``Crimson-osd`` currently uses the logging utility offered by Seastar. See ``src/common/dout.h`` for the mapping between Ceph logging levels to the severity levels in Seastar. For instance, messages sent to ``derr`` will be issued using ``logger::error()``, and the messages with a debug level greater than ``20`` will be issued using ``logger::trace()``. +---------+---------+ | ceph | seastar | +---------+---------+ | < 0 | error | +---------+---------+ | 0 | warn | +---------+---------+ | [1, 6) | info | +---------+---------+ | [6, 20] | debug | +---------+---------+ | > 20 | trace | +---------+---------+ Note that ``crimson-osd`` does not send log messages directly to a specified ``log_file``. It writes the logging messages to stdout and/or syslog. This behavior can be changed using ``--log-to-stdout`` and ``--log-to-syslog`` command line options. By default, ``log-to-stdout`` is enabled, and ``--log-to-syslog`` is disabled. vstart.sh --------- The following options aree handy when using ``vstart.sh``, ``--crimson`` Start ``crimson-osd`` instead of ``ceph-osd``. ``--nodaemon`` Do not daemonize the service. ``--redirect-output`` Redirect the ``stdout`` and ``stderr`` to ``out/$type.$num.stdout``. ``--osd-args`` Pass extra command line options to ``crimson-osd`` or ``ceph-osd``. This is useful for passing Seastar options to ``crimson-osd``. For example, one can supply ``--osd-args "--memory 2G"`` to set the amount of memory to use. Please refer to the output of:: crimson-osd --help-seastar for additional Seastar-specific command line options. ``--cyanstore`` Use CyanStore as the object store backend. ``--bluestore`` Use the alienized BlueStore as the object store backend. This is the default. ``--memstore`` Use the alienized MemStore as the object store backend. ``--seastore`` Use SeaStore as the back end object store. ``--seastore-devs`` Specify the block device used by SeaStore. ``--seastore-secondary-devs`` Optional. SeaStore supports multiple devices. Enable this feature by passing the block device to this option. ``--seastore-secondary-devs-type`` Optional. Specify the type of secondary devices. When the secondary device is slower than main device passed to ``--seastore-devs``, the cold data in faster device will be evicted to the slower devices over time. Valid types include ``HDD``, ``SSD``(default), ``ZNS``, and ``RANDOM_BLOCK_SSD`` Note secondary devices should not be faster than the main device. ``--seastore`` Use SeaStore as the object store backend. To start a cluster with a single Crimson node, run:: $ MGR=1 MON=1 OSD=1 MDS=0 RGW=0 ../src/vstart.sh -n -x \ --without-dashboard --cyanstore \ --crimson --redirect-output \ --osd-args "--memory 4G" Here we assign 4 GiB memory and a single thread running on core-0 to ``crimson-osd``. Another SeaStore example:: $ MGR=1 MON=1 OSD=1 MDS=0 RGW=0 ../src/vstart.sh -n -x \ --without-dashboard --seastore \ --crimson --redirect-output \ --seastore-devs /dev/sda \ --seastore-secondary-devs /dev/sdb \ --seastore-secondary-devs-type HDD Stop this ``vstart`` cluster by running:: $ ../src/stop.sh --crimson Metrics and Tracing =================== Crimson offers three ways to report stats and metrics. pg stats reported to mgr ------------------------ Crimson collects the per-pg, per-pool, and per-osd stats in a `MPGStats` message which is sent to the Ceph Managers. Manager modules can query them using the `MgrModule.get()` method. asock command ------------- An admin socket command is offered for dumping metrics:: $ ceph tell osd.0 dump_metrics $ ceph tell osd.0 dump_metrics reactor_utilization Here `reactor_utilization` is an optional string allowing us to filter the dumped metrics by prefix. Prometheus text protocol ------------------------ The listening port and address can be configured using the command line options of `--prometheus_port` see `Prometheus`_ for more details. .. _Prometheus: https://github.com/scylladb/seastar/blob/master/doc/prometheus.md Profiling Crimson ================= fio --- ``crimson-store-nbd`` exposes configurable ``FuturizedStore`` internals as an NBD server for use with ``fio``. In order to use ``fio`` to test ``crimson-store-nbd``, perform the below steps. #. You will need to install ``libnbd``, and compile it into ``fio`` .. prompt:: bash $ apt-get install libnbd-dev git clone git://git.kernel.dk/fio.git cd fio ./configure --enable-libnbd make #. Build ``crimson-store-nbd`` .. prompt:: bash $ cd build ninja crimson-store-nbd #. Run the ``crimson-store-nbd`` server with a block device. Specify the path to the raw device, for example ``/dev/nvme1n1``, in place of the created file for testing with a block device. .. prompt:: bash $ export disk_img=/tmp/disk.img export unix_socket=/tmp/store_nbd_socket.sock rm -f $disk_img $unix_socket truncate -s 512M $disk_img ./bin/crimson-store-nbd \ --device-path $disk_img \ --smp 1 \ --mkfs true \ --type transaction_manager \ --uds-path ${unix_socket} & Below are descriptions of these command line arguments: ``--smp`` The number of CPU cores to use (Symmetric MultiProcessor) ``--mkfs`` Initialize the device first. ``--type`` The back end to use. If ``transaction_manager`` is specified, SeaStore's ``TransactionManager`` and ``BlockSegmentManager`` are used to emulate a block device. Otherwise, this option is used to choose a backend of ``FuturizedStore``, where the whole "device" is divided into multiple fixed-size objects whose size is specified by ``--object-size``. So, if you are only interested in testing the lower-level implementation of SeaStore like logical address translation layer and garbage collection without the object store semantics, ``transaction_manager`` would be a better choice. #. Create a ``fio`` job file named ``nbd.fio`` .. code:: ini [global] ioengine=nbd uri=nbd+unix:///?socket=${unix_socket} rw=randrw time_based runtime=120 group_reporting iodepth=1 size=512M [job0] offset=0 #. Test the Crimson object store, using the custom ``fio`` built just now .. prompt:: bash $ ./fio nbd.fio CBT --- We can use `cbt`_ for performance tests:: $ git checkout main $ make crimson-osd $ ../src/script/run-cbt.sh --cbt ~/dev/cbt -a /tmp/baseline ../src/test/crimson/cbt/radosbench_4K_read.yaml $ git checkout yet-another-pr $ make crimson-osd $ ../src/script/run-cbt.sh --cbt ~/dev/cbt -a /tmp/yap ../src/test/crimson/cbt/radosbench_4K_read.yaml $ ~/dev/cbt/compare.py -b /tmp/baseline -a /tmp/yap -v 19:48:23 - INFO - cbt - prefill/gen8/0: bandwidth: (or (greater) (near 0.05)):: 0.183165/0.186155 => accepted 19:48:23 - INFO - cbt - prefill/gen8/0: iops_avg: (or (greater) (near 0.05)):: 46.0/47.0 => accepted 19:48:23 - WARNING - cbt - prefill/gen8/0: iops_stddev: (or (less) (near 0.05)):: 10.4403/6.65833 => rejected 19:48:23 - INFO - cbt - prefill/gen8/0: latency_avg: (or (less) (near 0.05)):: 0.340868/0.333712 => accepted 19:48:23 - INFO - cbt - prefill/gen8/1: bandwidth: (or (greater) (near 0.05)):: 0.190447/0.177619 => accepted 19:48:23 - INFO - cbt - prefill/gen8/1: iops_avg: (or (greater) (near 0.05)):: 48.0/45.0 => accepted 19:48:23 - INFO - cbt - prefill/gen8/1: iops_stddev: (or (less) (near 0.05)):: 6.1101/9.81495 => accepted 19:48:23 - INFO - cbt - prefill/gen8/1: latency_avg: (or (less) (near 0.05)):: 0.325163/0.350251 => accepted 19:48:23 - INFO - cbt - seq/gen8/0: bandwidth: (or (greater) (near 0.05)):: 1.24654/1.22336 => accepted 19:48:23 - INFO - cbt - seq/gen8/0: iops_avg: (or (greater) (near 0.05)):: 319.0/313.0 => accepted 19:48:23 - INFO - cbt - seq/gen8/0: iops_stddev: (or (less) (near 0.05)):: 0.0/0.0 => accepted 19:48:23 - INFO - cbt - seq/gen8/0: latency_avg: (or (less) (near 0.05)):: 0.0497733/0.0509029 => accepted 19:48:23 - INFO - cbt - seq/gen8/1: bandwidth: (or (greater) (near 0.05)):: 1.22717/1.11372 => accepted 19:48:23 - INFO - cbt - seq/gen8/1: iops_avg: (or (greater) (near 0.05)):: 314.0/285.0 => accepted 19:48:23 - INFO - cbt - seq/gen8/1: iops_stddev: (or (less) (near 0.05)):: 0.0/0.0 => accepted 19:48:23 - INFO - cbt - seq/gen8/1: latency_avg: (or (less) (near 0.05)):: 0.0508262/0.0557337 => accepted 19:48:23 - WARNING - cbt - 1 tests failed out of 16 Here we compile and run the same test against two branches: ``main`` and ``yet-another-pr``. We then compare the results. Along with every test case, a set of rules is defined to check for performance regressions when comparing the sets of test results. If a possible regression is found, the rule and corresponding test results are highlighted. .. _cbt: https://github.com/ceph/cbt Hacking Crimson =============== Seastar Documents ----------------- See `Seastar Tutorial `_ . Or build a browsable version and start an HTTP server:: $ cd seastar $ ./configure.py --mode debug $ ninja -C build/debug docs $ python3 -m http.server -d build/debug/doc/html You might want to install ``pandoc`` and other dependencies beforehand. Debugging Crimson ================= Debugging with GDB ------------------ The `tips`_ for debugging Scylla also apply to Crimson. .. _tips: https://github.com/scylladb/scylla/blob/master/docs/dev/debugging.md#tips-and-tricks Human-readable backtraces with addr2line ---------------------------------------- When a Seastar application crashes, it leaves us with a backtrace of addresses, like:: Segmentation fault. Backtrace: 0x00000000108254aa 0x00000000107f74b9 0x00000000105366cc 0x000000001053682c 0x00000000105d2c2e 0x0000000010629b96 0x0000000010629c31 0x00002a02ebd8272f 0x00000000105d93ee 0x00000000103eff59 0x000000000d9c1d0a /lib/x86_64-linux-gnu/libc.so.6+0x000000000002409a 0x000000000d833ac9 Segmentation fault The ``seastar-addr2line`` utility provided by Seastar can be used to map these addresses to functions. The script expects input on ``stdin``, so we need to copy and paste the above addresses, then send EOF by inputting ``control-D`` in the terminal. One might use ``echo`` or ``cat`` instead`:: $ ../src/seastar/scripts/seastar-addr2line -e bin/crimson-osd 0x00000000108254aa 0x00000000107f74b9 0x00000000105366cc 0x000000001053682c 0x00000000105d2c2e 0x0000000010629b96 0x0000000010629c31 0x00002a02ebd8272f 0x00000000105d93ee 0x00000000103eff59 0x000000000d9c1d0a 0x00000000108254aa [Backtrace #0] seastar::backtrace_buffer::append_backtrace() at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:1136 seastar::print_with_backtrace(seastar::backtrace_buffer&) at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:1157 seastar::print_with_backtrace(char const*) at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:1164 seastar::sigsegv_action() at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:5119 seastar::install_oneshot_signal_handler<11, &seastar::sigsegv_action>()::{lambda(int, siginfo_t*, void*)#1}::operator()(int, siginfo_t*, void*) const at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:5105 seastar::install_oneshot_signal_handler<11, &seastar::sigsegv_action>()::{lambda(int, siginfo_t*, void*)#1}::_FUN(int, siginfo_t*, void*) at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:5101 ?? ??:0 seastar::smp::configure(boost::program_options::variables_map, seastar::reactor_config) at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:5418 seastar::app_template::run_deprecated(int, char**, std::function&&) at /home/kefu/dev/ceph/build/../src/seastar/src/core/app-template.cc:173 (discriminator 5) main at /home/kefu/dev/ceph/build/../src/crimson/osd/main.cc:131 (discriminator 1) Note that ``seastar-addr2line`` is able to extract addresses from its input, so you can also paste the log messages as below:: 2020-07-22T11:37:04.500 INFO:teuthology.orchestra.run.smithi061.stderr:Backtrace: 2020-07-22T11:37:04.500 INFO:teuthology.orchestra.run.smithi061.stderr: 0x0000000000e78dbc 2020-07-22T11:37:04.501 INFO:teuthology.orchestra.run.smithi061.stderr: 0x0000000000e3e7f0 2020-07-22T11:37:04.501 INFO:teuthology.orchestra.run.smithi061.stderr: 0x0000000000e3e8b8 2020-07-22T11:37:04.501 INFO:teuthology.orchestra.run.smithi061.stderr: 0x0000000000e3e985 2020-07-22T11:37:04.501 INFO:teuthology.orchestra.run.smithi061.stderr: /lib64/libpthread.so.0+0x0000000000012dbf Unlike the classic ``ceph-osd``, Crimson does not print a human-readable backtrace when it handles fatal signals like `SIGSEGV` or `SIGABRT`. It is also more complicated with a stripped binary. So instead of planting a signal handler for those signals into Crimson, we can use `script/ceph-debug-docker.sh` to map addresses in the backtrace:: # assuming you are under the source tree of ceph $ ./src/script/ceph-debug-docker.sh --flavor crimson master:27e237c137c330ebb82627166927b7681b20d0aa centos:8 .... [root@3deb50a8ad51 ~]# wget -q https://raw.githubusercontent.com/scylladb/seastar/master/scripts/seastar-addr2line [root@3deb50a8ad51 ~]# dnf install -q -y file [root@3deb50a8ad51 ~]# python3 seastar-addr2line -e /usr/bin/crimson-osd # paste the backtrace here