Improve performance of large restore commands

I noticed a large (100MB) restore took hours to complete. The problem
is memory_xfer_partial repeatedly mallocs and memcpys the entire
100MB buffer for breakpoint shadow handling only to find a small
portion of it is actually written.

The testcase that originally took hours now takes 50 seconds.

gdb/
2013-07-29  Anton Blanchard  <anton@samba.org>

	* target.c (memory_xfer_partial): Cap write to 4KB.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 2d6a751..7d7a6fc 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,7 @@
+2013-11-04  Anton Blanchard  <anton@samba.org>
+
+       * target.c (memory_xfer_partial): Cap write to 4KB.
+
 2013-11-01  Tiago Stürmer Daitx  <tdaitx@linux.vnet.ibm.com>
 
        * breakpoint.c (create_longjmp_master_breakpoint): Allow libc

diff --git a/gdb/target.c b/gdb/target.c
index 22d7fb6..7aeab79 100644 (file)
--- a/gdb/target.c
+++ b/gdb/target.c
@@ -1678,6 +1678,13 @@ memory_xfer_partial (struct target_ops *ops, enum target_object object,
       void *buf;
       struct cleanup *old_chain;
 
+      /* A large write request is likely to be partially satisfied
+        by memory_xfer_partial_1.  We will continually malloc
+        and free a copy of the entire write request for breakpoint
+        shadow handling even though we only end up writing a small
+        subset of it.  Cap writes to 4KB to mitigate this.  */
+      len = min (4096, len);
+
       buf = xmalloc (len);
       old_chain = make_cleanup (xfree, buf);
       memcpy (buf, writebuf, len);