From: Max Kellermann <max.kellermann@ionos.com>
Date: Mon, 7 Oct 2024 19:11:31 +0000 (+0200)
Subject: common/Finisher: wake up after pushing to the queue
X-Git-Tag: v20.0.0~789^2~9
X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=0abad594d85f5ab9a5577810d2cd59dcf9a3d2ef;p=ceph.git

common/Finisher: wake up after pushing to the queue

Pushing to the queue may take a long time when the `std::vector` needs
to allocate more memory.  We should wake up the `Finisher` thread only
right before unlocking the `finisher_mutex` to reduce lock contention,
because it is the more likely that the mutex can really be acquired
when the thread really wakes up.

This imitates how commit cc7ec3e18d191575c did it - it refactored only
one of the `queue()` overloads, leaving less-than-optimal copies of
this piece code in all other overloads.

Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
---

diff --git a/src/common/Finisher.h b/src/common/Finisher.h
index 215930116d3..732ed746d56 100644
--- a/src/common/Finisher.h
+++ b/src/common/Finisher.h
@@ -83,12 +83,13 @@ class Finisher {
   auto queue(T &ls) -> decltype(std::distance(ls.begin(), ls.end()), void()) {
     {
       const std::lock_guard l{finisher_lock};
-      if (finisher_queue.empty() && !finisher_running) {
-	finisher_cond.notify_all();
-      }
+      const bool should_notify = finisher_queue.empty() && !finisher_running;
       for (Context *i : ls) {
 	finisher_queue.push_back(std::make_pair(i, 0));
       }
+      if (should_notify) {
+	finisher_cond.notify_all();
+      }
     }
     if (logger)
       logger->inc(l_finisher_queue_len, ls.size());