ircd::prof::psi: Add interface to poll for PSI linux>=5.2. (#144)

include/ircd/prof/psi.h

@@ -17,8 +17,12 @@ namespace ircd::prof::psi
 	struct metric;
 	struct refresh;
 
+	// Read and update the referenced extern.
 	bool refresh(file &) noexcept;
 
+	// Yield ircd::ctx until event; returns unrefreshed
+	file &wait();
+
 	extern const bool supported;
 	extern file cpu, mem, io;
 }

ircd/prof_linux.cc

@@ -188,6 +188,47 @@ ircd::prof::psi::io
 // prof::psi::metric::refresh
 //
 
+ircd::prof::psi::file &
+ircd::prof::psi::wait()
+try
+{
+	const fs::fd fd[3]
+	{
+		{ "/proc/pressure/cpu",    std::ios::in },
+		{ "/proc/pressure/memory", std::ios::in },
+		{ "/proc/pressure/io",     std::ios::in },
+	};
+
+	const size_t n
+	{
+		fs::select(fd)
+	};
+
+	switch(n)
+	{
+		case 0:  return cpu;
+		case 1:  return mem;
+		case 2:  return io;
+		default:
+			always_assert(false);
+			__builtin_unreachable();
+	}
+}
+catch(const ctx::interrupted &)
+{
+	throw;
+}
+catch(const std::exception &e)
+{
+	log::error
+	{
+		"Failed to poll pressure stall information :%s",
+		e.what(),
+	};
+
+	throw;
+}
+
 bool
 ircd::prof::psi::refresh(file &file)
 noexcept try

modules/console.cc

@@ -1278,9 +1278,33 @@ console_cmd__prof__psi(opt &out, const string_view &line)
 		out << std::endl;
 	}};
 
-	show_file("cpu", prof::psi::cpu);
-	show_file("mem", prof::psi::mem);
-	show_file("io ", prof::psi::io);
+	const params param{line, " ",
+	{
+		"file",
+	}};
+
+	string_view filename
+	{
+		param["file"]
+	};
+
+	if(filename == "wait")
+	{
+		auto &file(prof::psi::wait());
+		out << "Got: " << file.name;
+		out << std::endl << std::endl;
+		filename = file.name;
+	}
+
+	if(!filename || filename == "cpu")
+		show_file("cpu", prof::psi::cpu);
+
+	if(!filename || filename == "mem")
+		show_file("mem", prof::psi::mem);
+
+	if(!filename || filename == "io")
+		show_file("io ", prof::psi::io);
+
 	return true;
 }