diff options
| -rw-r--r-- | host/lib/usrp/device3/device3_io_impl.cpp | 30 |
1 files changed, 28 insertions, 2 deletions
diff --git a/host/lib/usrp/device3/device3_io_impl.cpp b/host/lib/usrp/device3/device3_io_impl.cpp index aa84dcab0..199cb2786 100644 --- a/host/lib/usrp/device3/device3_io_impl.cpp +++ b/host/lib/usrp/device3/device3_io_impl.cpp @@ -356,6 +356,8 @@ static bool tx_flow_ctrl( size_t fc_window, managed_buffer::sptr ) { + bool refresh_cache = false; + // Busy loop waiting for flow control update. This is necessary because // at this point there is data trying to be sent and it must be sent as // quickly as possible when the flow control update arrives to avoid @@ -363,6 +365,12 @@ static bool tx_flow_ctrl( // data needs to be sent and flow control is holding it back. while (true) { + if (refresh_cache) + { + // update the cached value from the atomic + fc_cache->last_seq_ack_cache = fc_cache->last_seq_ack; + } + // delta is the amount of FC credit we've used up const size_t delta = (fc_cache->last_seq_out & HW_SEQ_NUM_MASK) - (fc_cache->last_seq_ack_cache & HW_SEQ_NUM_MASK); @@ -373,8 +381,26 @@ static bool tx_flow_ctrl( fc_cache->last_seq_out++; //update seq return true; } - // update the cached value from the atomic - fc_cache->last_seq_ack_cache = fc_cache->last_seq_ack; + else + { + if (refresh_cache) + { + // We have already refreshed the cache and still + // lack flow control permission to send new data. + + // A true busy loop choked out the message handler + // thread on machines with processor limitations + // (too few cores). Yield to allow flow control + // receiver thread to operate. + boost::this_thread::yield(); + } + else + { + // Allow the cache to refresh and try again to + // see if the device has granted flow control permission. + refresh_cache = true; + } + } } return false; } |