Re: [PATCH] Improve performance of large restore commands

[Anton Blanchard <anton@samba.org>]

Hi Pedro,

> > 	* target.c (memory_xfer_partial): Cap write to 4kB.
> ...
> > +	 subset of it.  Cap writes to 4kB to mitigate this.  */
> ...
> 
> do write upper K, not k.  Lowercase k usually indicates decimal
> 10^3.  (see e.g.,
> http://en.wikipedia.org/wiki/Template:Bit_and_byte_prefixes).

Ahh sorry, I did that without thinking. Updated patch below.

Anton
--

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.

--

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

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

Index: b/gdb/target.c
===================================================================
--- a/gdb/target.c
+++ b/gdb/target.c
@@ -1669,6 +1669,13 @@ memory_xfer_partial (struct target_ops *
       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);