From ea30ee38f971df1001285623b23acd2894558a02 Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Sun, 23 Feb 2020 13:24:20 -0800
Subject: [PATCH] ircd::ctx: Optimize asio timer cancel action for ctx::wake().

---
 ircd/ctx.cc | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/ircd/ctx.cc b/ircd/ctx.cc
index e5aa496a7..e5d56a569 100644
--- a/ircd/ctx.cc
+++ b/ircd/ctx.cc
@@ -281,6 +281,40 @@ catch(const std::exception &e)
 	return false;
 }
 
+// Optimize ctx::wake() by reimplementing the timer cancel's op scheduler to
+// enqueue as a defer (private/priority queue) rather than to the post queue.
+#if defined(BOOST_ASIO_HAS_EPOLL)
+using epoll_time_traits = boost::asio::time_traits<boost::posix_time::ptime>;
+
+template<>
+inline std::size_t
+boost::asio::detail::epoll_reactor::cancel_timer(timer_queue<epoll_time_traits> &queue,
+                                                 typename timer_queue<epoll_time_traits>::per_timer_data &t,
+                                                 std::size_t max)
+{
+	std::size_t ret;
+	op_queue<operation> ops;
+	{
+		const mutex::scoped_lock lock(mutex_);
+		ret = queue.cancel_timer(t, ops, max);
+	}
+
+	auto *const thread_info
+	{
+		static_cast<scheduler_thread_info *>(scheduler::thread_call_stack::top())
+	};
+
+	for(auto *op(ops.front()); op; ops.pop(), op = ops.front())
+	{
+		static const bool is_continuation(true);
+		scheduler_.post_immediate_completion(op, is_continuation);
+		thread_info->private_outstanding_work -= is_continuation;
+	}
+
+	return ret;
+}
+#endif
+
 /// Throws if this context has been flagged for interruption and clears
 /// the flag.
 [[gnu::hot]]