From 369afe3124d5fc652e73e3d8ba9bcb7e04e5bca4 Mon Sep 17 00:00:00 2001
From: Avi Kivity <avi@scylladb.com>
Date: Thu, 23 Sep 2021 12:32:36 +0300
Subject: [PATCH] treewide: use coroutine::maybe_yield() instead of co_await
 make_ready_future()

The dedicated API shows the intent, and may be a tiny bit faster.

Closes #9382
---
 db/system_distributed_keyspace.cc      | 7 ++++---
 db/view/view.cc                        | 7 ++++---
 locator/token_metadata.cc              | 5 +++--
 reader_concurrency_semaphore.cc        | 3 ++-
 service/raft/raft_sys_table_storage.cc | 5 +++--
 sstables/partition_index_cache.hh      | 3 ++-
 sstables/sstables.cc                   | 5 +++--
 table.cc                               | 3 ++-
 test/raft/randomized_nemesis_test.cc   | 3 ++-
 utils/cached_file.hh                   | 3 ++-
 utils/logalloc.cc                      | 3 ++-
 11 files changed, 29 insertions(+), 18 deletions(-)

diff --git a/db/system_distributed_keyspace.cc b/db/system_distributed_keyspace.cc
index 6dc7172a5b..229115b396 100644
--- a/db/system_distributed_keyspace.cc
+++ b/db/system_distributed_keyspace.cc
@@ -39,6 +39,7 @@
 #include <seastar/core/shared_ptr.hh>
 #include <seastar/core/coroutine.hh>
 #include <seastar/core/future-util.hh>
+#include <seastar/coroutine/maybe_yield.hh>
 
 #include <boost/range/adaptor/transformed.hpp>
 
@@ -480,7 +481,7 @@ static future<utils::chunked_vector<mutation>> get_cdc_generation_mutations(
         res.back().set_cell(ckey, to_bytes("streams"), make_set_value(cdc_streams_set_type, std::move(streams)), ts);
         res.back().set_cell(ckey, to_bytes("ignore_msb"), int8_t(e.sharding_ignore_msb), ts);
 
-        co_await make_ready_future<>(); // maybe yield
+        co_await coroutine::maybe_yield();
     }
 
     co_return res;
@@ -577,7 +578,7 @@ static future<std::vector<mutation>> get_cdc_streams_descriptions_v2_mutation(
         res.back().set_cell(clustering_key::from_singular(*s, dht::token::to_int64(e.token_range_end)),
                 to_bytes("streams"), make_set_value(cdc_streams_set_type, std::move(streams)), ts);
 
-        co_await make_ready_future<>(); // maybe yield
+        co_await coroutine::maybe_yield();
     }
 
     co_return res;
@@ -694,7 +695,7 @@ system_distributed_keyspace::cdc_get_versioned_streams(db_clock::time_point not_
         utils::chunked_vector<cdc::stream_id> ids;
         for (auto& row : *streams_cql) {
             row.get_list_data<bytes>("streams", std::back_inserter(ids));
-            co_await make_ready_future<>(); // maybe yield
+            co_await coroutine::maybe_yield();
         }
 
         result.emplace(ts, cdc::streams_version{std::move(ids), ts});
diff --git a/db/view/view.cc b/db/view/view.cc
index c38ecc711f..6426212ae2 100644
--- a/db/view/view.cc
+++ b/db/view/view.cc
@@ -55,6 +55,7 @@
 
 #include <seastar/core/future-util.hh>
 #include <seastar/core/coroutine.hh>
+#include <seastar/coroutine/maybe_yield.hh>
 
 #include "database.hh"
 #include "clustering_bounds_comparator.hh"
@@ -1138,7 +1139,7 @@ future<query::clustering_row_ranges> calculate_affected_clustering_ranges(const
             }
             for (auto&& r : v.view->view_info()->partition_slice().default_row_ranges()) {
                 view_row_ranges.push_back(r.transform(std::mem_fn(&clustering_key_prefix::view)));
-                co_await make_ready_future<>(); // yield if needed
+                co_await coroutine::maybe_yield();
             }
         }
     }
@@ -1155,7 +1156,7 @@ future<query::clustering_row_ranges> calculate_affected_clustering_ranges(const
                 if (overlap) {
                     row_ranges.push_back(std::move(overlap).value());
                 }
-                co_await make_ready_future<>(); // yield if needed
+                co_await coroutine::maybe_yield();
             }
         }
     }
@@ -1164,7 +1165,7 @@ future<query::clustering_row_ranges> calculate_affected_clustering_ranges(const
         if (update_requires_read_before_write(base, views, key, row)) {
             row_ranges.emplace_back(row.key());
         }
-        co_await make_ready_future<>(); // yield if needed
+        co_await coroutine::maybe_yield();
     }
 
     // Note that the views could have restrictions on regular columns,
diff --git a/locator/token_metadata.cc b/locator/token_metadata.cc
index e0b0270d85..d4053245a9 100644
--- a/locator/token_metadata.cc
+++ b/locator/token_metadata.cc
@@ -31,6 +31,7 @@
 #include <boost/icl/interval.hpp>
 #include <boost/icl/interval_map.hpp>
 #include <seastar/core/coroutine.hh>
+#include <seastar/coroutine/maybe_yield.hh>
 #include <boost/range/adaptors.hpp>
 #include "utils/stall_free.hh"
 
@@ -481,7 +482,7 @@ future<> token_metadata_impl::update_normal_tokens(const std::unordered_map<inet
         }
 
         for(auto it = _token_to_endpoint_map.begin(), ite = _token_to_endpoint_map.end(); it != ite;) {
-            co_await make_ready_future<>(); // maybe yield
+            co_await coroutine::maybe_yield();
             if(it->second == endpoint) {
                 it = _token_to_endpoint_map.erase(it);
             } else {
@@ -495,7 +496,7 @@ future<> token_metadata_impl::update_normal_tokens(const std::unordered_map<inet
         invalidate_cached_rings();
         for (const token& t : tokens)
         {
-            co_await make_ready_future<>(); // maybe yield
+            co_await coroutine::maybe_yield();
             auto prev = _token_to_endpoint_map.insert(std::pair<token, inet_address>(t, endpoint));
             should_sort_tokens |= prev.second; // new token inserted -> sort
             if (prev.first->second != endpoint) {
diff --git a/reader_concurrency_semaphore.cc b/reader_concurrency_semaphore.cc
index 50ae2dd0af..c6534e89bd 100644
--- a/reader_concurrency_semaphore.cc
+++ b/reader_concurrency_semaphore.cc
@@ -24,6 +24,7 @@
 #include <seastar/util/lazy.hh>
 #include <seastar/util/log.hh>
 #include <seastar/core/coroutine.hh>
+#include <seastar/coroutine/maybe_yield.hh>
 
 #include "reader_concurrency_semaphore.hh"
 #include "utils/exceptions.hh"
@@ -618,7 +619,7 @@ future<> reader_concurrency_semaphore::execution_loop() noexcept {
             }
 
             if (need_preempt()) {
-                co_await make_ready_future<>();
+                co_await coroutine::maybe_yield();
             }
         }
     }
diff --git a/service/raft/raft_sys_table_storage.cc b/service/raft/raft_sys_table_storage.cc
index 12f1bbdcd7..647836c5f4 100644
--- a/service/raft/raft_sys_table_storage.cc
+++ b/service/raft/raft_sys_table_storage.cc
@@ -37,6 +37,7 @@
 
 #include <seastar/core/loop.hh>
 #include <seastar/core/coroutine.hh>
+#include <seastar/coroutine/maybe_yield.hh>
 
 namespace service {
 
@@ -97,7 +98,7 @@ future<raft::log_entries> raft_sys_table_storage::load_log() {
         log.emplace_back(make_lw_shared<const raft::log_entry>(
             raft::log_entry{.term = term, .idx = idx, .data = std::move(data)}));
 
-        co_await make_ready_future<>();
+        co_await coroutine::maybe_yield();
     }
     co_return log;
 }
@@ -227,7 +228,7 @@ future<> raft_sys_table_storage::do_store_log_entries(const std::vector<raft::lo
                 fragmented_temporary_buffer::view(stmt_data_views.back())));
         stmt_value_views.emplace_back(std::move(value_views));
 
-        co_await make_ready_future<>();
+        co_await coroutine::maybe_yield();
     }
 
     auto batch_options = cql3::query_options::make_batch_options(
diff --git a/sstables/partition_index_cache.hh b/sstables/partition_index_cache.hh
index 2d808cb244..eae21bf1db 100644
--- a/sstables/partition_index_cache.hh
+++ b/sstables/partition_index_cache.hh
@@ -26,6 +26,7 @@
 #include <seastar/core/future.hh>
 #include <seastar/core/loop.hh>
 #include <seastar/core/coroutine.hh>
+#include <seastar/coroutine/maybe_yield.hh>
 #include "utils/loading_shared_values.hh"
 #include "utils/chunked_vector.hh"
 #include "utils/bptree.hh"
@@ -274,7 +275,7 @@ public:
             });
             if (need_preempt() && i != _cache.end()) {
                 auto key = i->key();
-                co_await make_ready_future<>();
+                co_await coroutine::maybe_yield();
                 i = _cache.lower_bound(key);
             }
         }
diff --git a/sstables/sstables.cc b/sstables/sstables.cc
index 1e303b3239..cb38bc2808 100644
--- a/sstables/sstables.cc
+++ b/sstables/sstables.cc
@@ -37,6 +37,7 @@
 #include <seastar/util/closeable.hh>
 #include <iterator>
 #include <seastar/core/coroutine.hh>
+#include <seastar/coroutine/maybe_yield.hh>
 
 #include "dht/sharder.hh"
 #include "types.hh"
@@ -521,7 +522,7 @@ future<> parse(const schema& schema, sstable_version_types v, random_access_read
     while (s.positions.size() != s.header.size) {
         s.positions.push_back(seastar::read_le<pos_type>(b));
         b += sizeof(pos_type);
-        co_await make_ready_future<>(); // yield
+        co_await coroutine::maybe_yield();
     }
     // Since the keys in the index are not sized, we need to calculate
     // the start position of the index i+1 to determine the boundaries
@@ -682,7 +683,7 @@ future<> parse(const schema& s, sstable_version_types v, random_access_reader& i
             eh.bucket_offsets.push_back(offset);
         }
         eh.buckets.push_back(bucket);
-        co_await make_ready_future<>(); // yield
+        co_await coroutine::maybe_yield();
     }
 }
 
diff --git a/table.cc b/table.cc
index 28e05f2d93..6c76748cd0 100644
--- a/table.cc
+++ b/table.cc
@@ -21,6 +21,7 @@
 
 #include <seastar/core/seastar.hh>
 #include <seastar/core/coroutine.hh>
+#include <seastar/coroutine/maybe_yield.hh>
 #include <seastar/util/closeable.hh>
 
 #include "database.hh"
@@ -762,7 +763,7 @@ table::sstable_list_builder::build_new_list(const sstables::sstable_set& current
         if (!s.contains(tab)) {
             new_sstable_list.insert(tab);
         }
-        co_await make_ready_future<>(); // yield if needed.
+        co_await coroutine::maybe_yield();
     }
     co_return make_lw_shared<sstables::sstable_set>(std::move(new_sstable_list));
 }
diff --git a/test/raft/randomized_nemesis_test.cc b/test/raft/randomized_nemesis_test.cc
index 71a8252b93..2f7a566f3a 100644
--- a/test/raft/randomized_nemesis_test.cc
+++ b/test/raft/randomized_nemesis_test.cc
@@ -23,6 +23,7 @@
 #include <seastar/testing/test_case.hh>
 #include <seastar/core/timed_out_error.hh>
 #include <seastar/core/coroutine.hh>
+#include <seastar/coroutine/maybe_yield.hh>
 #include <seastar/core/gate.hh>
 #include <seastar/core/queue.hh>
 #include <seastar/core/future-util.hh>
@@ -146,7 +147,7 @@ public:
                     // In any case we simply drop the output.
                 }
 
-                co_await make_ready_future<>(); // maybe yield
+                co_await coroutine::maybe_yield();
             }
         });
     }
diff --git a/utils/cached_file.hh b/utils/cached_file.hh
index 8d6d58d6bf..9cb542c370 100644
--- a/utils/cached_file.hh
+++ b/utils/cached_file.hh
@@ -29,6 +29,7 @@
 
 #include <seastar/core/file.hh>
 #include <seastar/core/coroutine.hh>
+#include <seastar/coroutine/maybe_yield.hh>
 
 #include <map>
 
@@ -460,7 +461,7 @@ public:
             }
             if (need_preempt() && i != _cache.end()) {
                 auto key = i->idx;
-                co_await make_ready_future<>();
+                co_await coroutine::maybe_yield();
                 i = _cache.lower_bound(key);
             }
         }
diff --git a/utils/logalloc.cc b/utils/logalloc.cc
index 1a2e7dd0de..ff9befbb69 100644
--- a/utils/logalloc.cc
+++ b/utils/logalloc.cc
@@ -35,6 +35,7 @@
 #include <seastar/core/metrics.hh>
 #include <seastar/core/reactor.hh>
 #include <seastar/core/coroutine.hh>
+#include <seastar/coroutine/maybe_yield.hh>
 #include <seastar/core/with_scheduling_group.hh>
 #include <seastar/util/alloc_failure_injector.hh>
 #include <seastar/util/backtrace.hh>
@@ -413,7 +414,7 @@ private:
                 break;
             }
             _reclaim(free_memory_threshold - memory::stats().free_memory());
-            co_await make_ready_future<>();
+            co_await coroutine::maybe_yield();
         }
         llogger.debug("background_reclaimer::main_loop: exit");
     }