From e6a71efe8c471aba642e407e1436eb81c4e345d6 Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Fri, 15 Oct 2021 14:57:31 -0700
Subject: [PATCH] ircd::cl: Sample tsc for work item submission for blocking
 interface mitigations.

---
 include/ircd/cl.h |  1 +
 ircd/cl.cc        | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/include/ircd/cl.h b/include/ircd/cl.h
index 95e9002eb..d900069bb 100644
--- a/include/ircd/cl.h
+++ b/include/ircd/cl.h
@@ -58,6 +58,7 @@ struct ircd::cl::work
 	void *handle {nullptr};
 	ctx::ctx *context {ctx::current};
 	void *object {nullptr};
+	uint64_t ts {ircd::cycles()};
 
 	static void init(), fini() noexcept;
 
diff --git a/ircd/cl.cc b/ircd/cl.cc
index 7d9149b66..37ff6e43e 100644
--- a/ircd/cl.cc
+++ b/ircd/cl.cc
@@ -655,6 +655,7 @@ namespace ircd::cl
 	static const size_t _deps_list_max {32};
 	static thread_local cl_event _deps_list[_deps_list_max];
 
+	static void check_submit_blocking(cl::exec *const &, const exec::opts &);
 	static void handle_submitted(cl::exec *const &, const exec::opts &);
 	static vector_view<cl_event> make_deps_default(cl::work *const &, const exec::opts &);
 	static vector_view<cl_event> make_deps(cl::work *const &, const exec::opts &);
@@ -1057,6 +1058,7 @@ try
 		assert(this->handle);
 		call(clReleaseEvent, cl_event(this->handle));
 		this->handle = nullptr;
+		this->work::ts = ircd::cycles();
 	}};
 
 	// Wait for the mapping to complete before presenting the buffer.
@@ -1171,6 +1173,7 @@ try
 		assert(this->handle);
 		call(clReleaseEvent, cl_event(this->handle));
 		this->handle = nullptr;
+		this->work::ts = ircd::cycles();
 	}};
 
 	wait();
@@ -1202,6 +1205,9 @@ ircd::cl::handle_submitted(cl::exec *const &exec,
 	if(opts.sync)
 		cl::sync();
 
+	if(likely(!opts.blocking))
+		check_submit_blocking(exec, opts);
+
 	if(opts.nice == 0)
 		ctx::yield();
 
@@ -1209,6 +1215,38 @@ ircd::cl::handle_submitted(cl::exec *const &exec,
 		ctx::sleep(opts.nice * milliseconds(nice_rate));
 }
 
+void
+ircd::cl::check_submit_blocking(cl::exec *const &exec,
+                                const exec::opts &opts)
+{
+	const auto threshold
+	{
+		268'435'456
+	};
+
+	const auto submit_cycles
+	{
+		prof::cycles() - exec->ts
+	};
+
+	if(likely(submit_cycles < threshold))
+		return;
+
+	char nbuf[64];
+	const auto name
+	{
+		exec->name(nbuf)
+	};
+
+	char pbuf[32];
+	log::dwarning
+	{
+		log, "clEnqueue() kernel '%s' blocking the host for %s cycles on submit.",
+		name?: "<unamed or data transfer kernel>"_sv,
+		pretty(pbuf, si(submit_cycles), 1),
+	};
+}
+
 ircd::vector_view<cl_event>
 ircd::cl::make_deps(cl::work *const &work,
                     const exec::opts &opts)