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 class io_queue;
  33 using io_priority_class_id = unsigned;
  34 // We could very well just add the name to the io_priority_class. However, because that
  35 // structure is passed along all the time - and sometimes we can't help but copy it, better keep
  36 // it lean. The name won't really be used for anything other than monitoring.
  37 class io_priority_class {
  38     io_priority_class_id _id;
  39
  40     io_priority_class() = delete;
  41     explicit io_priority_class(io_priority_class_id id) noexcept
  42         : _id(id)
  43     { }
  44
  45     bool rename_registered(sstring name);
  46
  47 public:
  48     io_priority_class_id id() const noexcept {
  49         return _id;
  50     }
  51
  52     static io_priority_class register_one(sstring name, uint32_t shares);
  53
  54     /// \brief Updates the current amount of shares for a given priority class
  55     ///
  56     /// \param pc the priority class handle
  57     /// \param shares the new shares value
  58     /// \return a future that is ready when the share update is applied
  59     future<> update_shares(uint32_t shares) const;
  60
  61     /// \brief Updates the current bandwidth for a given priority class
  62     ///
  63     /// The bandwidth applied is NOT shard-local, instead it is applied so that
  64     /// all shards cannot consume more bytes-per-second altogether
  65     ///
  66     /// \param bandwidth the new bandwidth value in bytes/second
  67     /// \return a future that is ready when the bandwidth update is applied
  68     future<> update_bandwidth(uint64_t bandwidth) const;
  69
  70     /// Renames an io priority class
  71     ///
  72     /// Renames an `io_priority_class` previously created with register_one_priority_class().
  73     ///
  74     /// The operation is global and affects all shards.
  75     /// The operation affects the exported statistics labels.
  76     ///
  77     /// \param pc The io priority class to be renamed
  78     /// \param new_name The new name for the io priority class
  79     /// \return a future that is ready when the io priority class have been renamed
  80     future<> rename(sstring new_name) noexcept;
  81
  82     unsigned get_shares() const;
  83     sstring get_name() const;
  84
  85 private:
  86     struct class_info {
  87         unsigned shares = 0;
  88         sstring name;
  89         bool registered() const noexcept { return shares != 0; }
  90     };
  91
  92     static constexpr unsigned _max_classes = 2048;
  93     static std::mutex _register_lock;
  94     static std::array<class_info, _max_classes> _infos;
  95 };
  96
  97 const io_priority_class& default_priority_class();
  98
  99 } // namespace seastar