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Re: [PATCH] Improve performance of large restore commands
- From: Anton Blanchard <anton at samba dot org>
- To: Pedro Alves <palves at redhat dot com>
- Cc: Luis Machado <lgustavo at codesourcery dot com>, gdb-patches at sourceware dot org
- Date: Tue, 30 Jul 2013 09:24:58 +1000
- Subject: Re: [PATCH] Improve performance of large restore commands
- References: <20130725220858 dot 58184193 at kryten> <51F16780 dot 70408 at redhat dot com> <20130729154457 dot 0e6e6bd7 at kryten> <51F6789B dot 3090404 at redhat dot com>
Hi Pedro,
Thanks for the comments!
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);