gdb_server: improved gdb load performance

by ack'ing memory writes immediately and reporting either
at next memory write or stepi/continue time. GDB will then
send off a new packet that is ready by the time the previous
packet has been written to target memory.

On faster adapters this can be as much as 10% improvement.

Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

diff --git a/src/server/gdb_server.c b/src/server/gdb_server.c
index 17ca4398e6b3977f5b57061895d994a7cb789f4c..f46980e14f57c7c08a14fad758cec5dc3ecfb688 100644 (file)
--- a/src/server/gdb_server.c
+++ b/src/server/gdb_server.c
@@ -2,7 +2,7 @@
  *   Copyright (C) 2005 by Dominic Rath                                    *
  *   Dominic.Rath@gmx.de                                                   *
  *                                                                         *
- *   Copyright (C) 2007-2009 Øyvind Harboe                                 *
+ *   Copyright (C) 2007-2010 Øyvind Harboe                                 *
  *   oyvind.harboe@zylin.com                                               *
  *                                                                         *
  *   Copyright (C) 2008 by Spencer Oliver                                  *
@@ -61,7 +61,12 @@ struct gdb_connection
        bool sync;      /* set flag to true if you want the next stepi to return immediately.
                       allowing GDB to pick up a fresh set of register values from the target
                       without modifying the target state. */
-
+       /* We delay reporting memory write errors until next step/continue or memory
+        * write. This improves performance of gdb load significantly as the GDB packet
+        * can be replied immediately and a new GDB packet will be ready without delay
+        * (ca. 10% or so...).
+        */
+       bool mem_write_error;
 };
 
 
@@ -821,6 +826,7 @@ static int gdb_new_connection(struct connection *connection)
        gdb_connection->busy = 0;
        gdb_connection->noack_mode = 0;
        gdb_connection->sync = true;
+       gdb_connection->mem_write_error = false;
 
        /* send ACK to GDB for debug request */
        gdb_write(connection, "+", 1);
@@ -1361,7 +1367,7 @@ static int gdb_write_memory_binary_packet(struct connection *connection,
        uint32_t addr = 0;
        uint32_t len = 0;
 
-       int retval;
+       int retval = ERROR_OK;
 
        /* skip command character */
        packet++;
@@ -1382,14 +1388,18 @@ static int gdb_write_memory_binary_packet(struct connection *connection,
                return ERROR_SERVER_REMOTE_CLOSED;
        }
 
-       retval = ERROR_OK;
-       if (len)
-       {
-               LOG_DEBUG("addr: 0x%8.8" PRIx32 ", len: 0x%8.8" PRIx32 "", addr, len);
+       struct gdb_connection *gdb_connection = connection->priv;
 
-               retval = target_write_buffer(target, addr, len, (uint8_t*)separator);
+       if (gdb_connection->mem_write_error)
+       {
+               retval = ERROR_FAIL;
+               /* now that we have reported the memory write error, we can clear the condition */
+               gdb_connection->mem_write_error = false;
        }
 
+       /* By replying the packet *immediately* GDB will send us a new packet
+        * while we write the last one to the target.
+        */
        if (retval == ERROR_OK)
        {
                gdb_put_packet(connection, "OK", 2);
@@ -1400,6 +1410,17 @@ static int gdb_write_memory_binary_packet(struct connection *connection,
                        return retval;
        }
 
+       if (len)
+       {
+               LOG_DEBUG("addr: 0x%8.8" PRIx32 ", len: 0x%8.8" PRIx32 "", addr, len);
+
+               retval = target_write_buffer(target, addr, len, (uint8_t*)separator);
+               if (retval != ERROR_OK)
+               {
+                       gdb_connection->mem_write_error = true;
+               }
+       }
+
        return ERROR_OK;
 }
 
@@ -2211,6 +2232,14 @@ static int gdb_input_inner(struct connection *connection)
                                                struct gdb_connection *gdb_con = connection->priv;
                                                log_add_callback(gdb_log_callback, connection);
 
+                                               if (gdb_con->mem_write_error)
+                                               {
+                                                       LOG_ERROR("Memory write failure!");
+
+                                                       /* now that we have reported the memory write error, we can clear the condition */
+                                                       gdb_con->mem_write_error = false;
+                                               }
+
                                                bool nostep = false;
                                                bool already_running = false;
                                                if (target->state == TARGET_RUNNING)