From 597e7965a7bd9a0fc76a5acbaf260b05e42c474c Mon Sep 17 00:00:00 2001
From: Michael West <michael.west@ettus.com>
Date: Fri, 8 Nov 2013 15:30:03 -0800
Subject: BUG #183:  B200 High CPU Usage:  Created a single thread to handle
 libusb events and expanded packet size to 16k

---
 host/lib/transport/libusb1_base.cpp | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

(limited to 'host/lib/transport/libusb1_base.cpp')

diff --git a/host/lib/transport/libusb1_base.cpp b/host/lib/transport/libusb1_base.cpp
index 0ef53db0a..4cf3ea17d 100644
--- a/host/lib/transport/libusb1_base.cpp
+++ b/host/lib/transport/libusb1_base.cpp
@@ -19,10 +19,12 @@
 #include <uhd/exception.hpp>
 #include <uhd/utils/msg.hpp>
 #include <uhd/utils/log.hpp>
+#include <uhd/utils/tasks.hpp>
 #include <uhd/types/dict.hpp>
 #include <boost/weak_ptr.hpp>
 #include <boost/thread/mutex.hpp>
 #include <boost/foreach.hpp>
+#include <boost/bind.hpp>
 #include <cstdlib>
 #include <iostream>
 
@@ -37,9 +39,11 @@ public:
     libusb_session_impl(void){
         UHD_ASSERT_THROW(libusb_init(&_context) == 0);
         libusb_set_debug(_context, debug_level);
+        task_handler = task::make(boost::bind(&libusb_session_impl::libusb_event_handler_task, this, _context));
     }
 
     ~libusb_session_impl(void){
+        task_handler.reset();
         libusb_exit(_context);
     }
 
@@ -49,6 +53,21 @@ public:
 
 private:
     libusb_context *_context;
+    task::sptr task_handler;
+
+    /*
+     * Task to handle libusb events.  There should only be one thread per libusb_context handling events.
+     * Using more than one thread can result in excessive CPU usage in kernel space (presumably from locking/waiting).
+     * The libusb documentation says it is safe, which it is, but it neglects to state the cost in CPU usage.
+     * Just don't do it!
+     */
+    UHD_INLINE void libusb_event_handler_task(libusb_context *context)
+    {
+        timeval tv;
+        tv.tv_sec = 0;
+        tv.tv_usec = 100000;
+        libusb_handle_events_timeout(context, &tv);
+    }
 };
 
 libusb::session::sptr libusb::session::get_global_session(void){
-- 
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