ceph/src/seastar/include/seastar/core/io_priority_class.hh

   1 /*
   2  * This file is open source software, licensed to you under the terms
   3  * of the Apache License, Version 2.0 (the "License").  See the NOTICE file
   4  * distributed with this work for additional information regarding copyright
   5  * ownership.  You may not use this file except in compliance with the License.
   6  *
   7  * You may obtain a copy of the License at
   8  *
   9  *   http://www.apache.org/licenses/LICENSE-2.0
  10  *
  11  * Unless required by applicable law or agreed to in writing,
  12  * software distributed under the License is distributed on an
  13  * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  14  * KIND, either express or implied.  See the License for the
  15  * specific language governing permissions and limitations
  16  * under the License.
  17  */
  18 /*
  19  * Copyright 2021 ScyllaDB
  20  */
  21
  22 #pragma once
  23
  24 #include <seastar/core/sstring.hh>
  25 #include <seastar/core/future.hh>
  26
  27 #include <array>
  28 #include <mutex>
  29
  30 namespace seastar {
  31
  32 /// \cond internal
  33 class io_queue;
  34 using io_priority_class_id = unsigned;
  35 // We could very well just add the name to the io_priority_class. However, because that
  36 // structure is passed along all the time - and sometimes we can't help but copy it, better keep
  37 // it lean. The name won't really be used for anything other than monitoring.
  38 class io_priority_class {
  39     io_priority_class_id _id;
  40
  41     io_priority_class() = delete;
  42     explicit io_priority_class(io_priority_class_id id) noexcept
  43         : _id(id)
  44     { }
  45
  46     bool rename_registered(sstring name);
  47
  48 public:
  49     io_priority_class_id id() const noexcept {
  50         return _id;
  51     }
  52
  53     static io_priority_class register_one(sstring name, uint32_t shares);
  54
  55     /// \brief Updates the current amount of shares for a given priority class
  56     ///
  57     /// \param pc the priority class handle
  58     /// \param shares the new shares value
  59     /// \return a future that is ready when the share update is applied
  60     future<> update_shares(uint32_t shares) const;
  61
  62     /// Renames an io priority class
  63     ///
  64     /// Renames an `io_priority_class` previously created with register_one_priority_class().
  65     ///
  66     /// The operation is global and affects all shards.
  67     /// The operation affects the exported statistics labels.
  68     ///
  69     /// \param pc The io priority class to be renamed
  70     /// \param new_name The new name for the io priority class
  71     /// \return a future that is ready when the io priority class have been renamed
  72     future<> rename(sstring new_name) noexcept;
  73
  74     unsigned get_shares() const;
  75     sstring get_name() const;
  76
  77 private:
  78     struct class_info {
  79         unsigned shares = 0;
  80         sstring name;
  81         bool registered() const noexcept { return shares != 0; }
  82     };
  83
  84     static constexpr unsigned _max_classes = 2048;
  85     static std::mutex _register_lock;
  86     static std::array<class_info, _max_classes> _infos;
  87 };
  88
  89 const io_priority_class& default_priority_class();
  90
  91 } // namespace seastar