Re: [PATCH 2/3] set/show code-cache

Yao Qi
2013-11-21T03:05:47Z

I update this patch for the name of some variables, after we discussed
in patch 1/3. I'll commit it in two days.

--
Yao (é½å°§)

gdb:

2013-11-21 Yao Qi <yao@codesourcery.com>

* NEWS: Add note on new "set code-cache" option.
* target-dcache.c (code_cache_enabled_1): New variable.
(code_cache_enabled): New variable.
(show_code_cache, set_code_cache): New function.
(code_cache_enabled_p): New function.
(_initialize_target_dcache): Register command.
* target-dcache.h (code_cache_enabled_p): Declare.
* target.c (memory_xfer_partial_1):Handle
TARGET_OBJECT_CODE_MEMORY and code_cache_enabled.
(target_read_code): New function.
* target.h (enum target_object) <TARGET_OBJECT_CODE_MEMORY>:
New.
(target_read_code): Declare.

gdb/doc:

2013-11-21 Yao Qi <yao@codesourcery.com>

* gdb.texinfo (Caching Remote Data): Document new
`set/show stack-cache' option.
---
gdb/NEWS | 6 +++++
gdb/doc/gdb.texinfo | 16 ++++++++++++++-
gdb/target-dcache.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++++++
gdb/target-dcache.h | 2 +
gdb/target.c | 23 ++++++++++++++++++---
gdb/target.h | 5 ++++
6 files changed, 99 insertions(+), 5 deletions(-)

diff --git a/gdb/NEWS b/gdb/NEWS
index 9fc3638..86a9d63 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -117,6 +117,12 @@ show startup-with-shell
Specifies whether Unix child processes are started via a shell or
directly.

+set code-cache
+show code-cache
+ Use the target memory cache for accesses to the code segment. This
+ improves performance of remote debugging (particularly disassembly)
+ without affecting correctness.
+
* You can now use a literal value 'unlimited' for options that
interpret 0 or -1 as meaning "unlimited". E.g., "set
trace-buffer-size unlimited" is now an alias for "set
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index d1fa6c8..9e64dd2 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -10842,7 +10842,8 @@ Therefore, by default, @value{GDBN} only caches data
known to be on the stack@footnote{In non-stop mode, it is moderately
rare for a running thread to modify the stack of a stopped thread
in a way that would interfere with a backtrace, and caching of
-stack reads provides a significant speed up of remote backtraces.}.
+stack reads provides a significant speed up of remote backtraces.} or
+in the code segment.
Other regions of memory can be explicitly marked as
cacheable; @pxref{Memory Region Attributes}.

@@ -10867,6 +10868,19 @@ caching. By default, this option is @code{ON}.
@item show stack-cache
Show the current state of data caching for memory accesses.

+@kindex set code-cache
+@item set code-cache on
+@itemx set code-cache off
+Enable or disable caching of code segment accesses. When @code{ON},
+use caching. By default, this option is @code{ON}. This improves
+performance of disassembly in remote debugging without affecting
+correctness.
+
+@kindex show code-cache
+@item show code-cache
+Show the current state of target memory cache for code segment
+accesses.
+
@kindex info dcache
@item info dcache @r{[}line@r{]}
Print the information about the performance of data cache of the
diff --git a/gdb/target-dcache.c b/gdb/target-dcache.c
index 6b7986a..25b2a85 100644
--- a/gdb/target-dcache.c
+++ b/gdb/target-dcache.c
@@ -124,6 +124,46 @@ stack_cache_enabled_p (void)
return stack_cache_enabled;
}

+/* The option sets this. */
+
+static int code_cache_enabled_1 = 1;
+
+/* And set_code_cache updates this.
+ The reason for the separation is so that we don't flush the cache for
+ on->on transitions. */
+static int code_cache_enabled = 1;
+
+/* This is called *after* the code-cache has been set.
+ Flush the cache for off->on and on->off transitions.
+ There's no real need to flush the cache for on->off transitions,
+ except cleanliness. */
+
+static void
+set_code_cache (char *args, int from_tty, struct cmd_list_element *c)
+{
+ if (code_cache_enabled != code_cache_enabled_1)
+ target_dcache_invalidate ();
+
+ code_cache_enabled = code_cache_enabled_1;
+}
+
+/* Show option "code-cache". */
+
+static void
+show_code_cache (struct ui_file *file, int from_tty,
+ struct cmd_list_element *c, const char *value)
+{
+ fprintf_filtered (file, _("Cache use for code accesses is %s.\n"), value);
+}
+
+/* Return true if "code cache" is enabled, otherwise, return false. */
+
+int
+code_cache_enabled_p (void)
+{
+ return code_cache_enabled;
+}
+
/* -Wmissing-prototypes */
extern initialize_file_ftype _initialize_target_dcache;

@@ -141,6 +181,18 @@ By default, caching for stack access is on."),
show_stack_cache,
&setlist, &showlist);

+ add_setshow_boolean_cmd ("code-cache", class_support,
+ &code_cache_enabled_1, _("\
+Set cache use for code segment access."), _("\
+Show cache use for code segment access."), _("\
+When on, use the target memory cache for all code segment access,\n\
+regardless of any configured memory regions. This improves remote\n\
+performance significantly. By default, caching for code segment\n\
+access is on."),
+ set_code_cache,
+ show_code_cache,
+ &setlist, &showlist);
+
target_dcache_aspace_key
= register_address_space_data_with_cleanup (NULL,
target_dcache_cleanup);
diff --git a/gdb/target-dcache.h b/gdb/target-dcache.h
index 3200dd9..59e0b3d 100644
--- a/gdb/target-dcache.h
+++ b/gdb/target-dcache.h
@@ -30,4 +30,6 @@ extern int target_dcache_init_p (void);

extern int stack_cache_enabled_p (void);

+extern int code_cache_enabled_p (void);
+
#endif /* TARGET_DCACHE_H */
diff --git a/gdb/target.c b/gdb/target.c
index f402a18..cc6194b 100644
--- a/gdb/target.c
+++ b/gdb/target.c
@@ -1547,7 +1547,8 @@ memory_xfer_partial_1 (struct target_ops *ops, enum target_object object,
the collected memory range fails. */
&& get_traceframe_number () == -1
&& (region->attrib.cache
- || (stack_cache_enabled_p () && object == TARGET_OBJECT_STACK_MEMORY)))
+ || (stack_cache_enabled_p () && object == TARGET_OBJECT_STACK_MEMORY)
+ || (code_cache_enabled_p () && object == TARGET_OBJECT_CODE_MEMORY)))
{
DCACHE *dcache = target_dcache_get_or_init ();

@@ -1600,8 +1601,8 @@ memory_xfer_partial_1 (struct target_ops *ops, enum target_object object,
&& writebuf != NULL
&& target_dcache_init_p ()
&& !region->attrib.cache
- && stack_cache_enabled_p ()
- && object != TARGET_OBJECT_STACK_MEMORY)
+ && ((stack_cache_enabled_p () && object != TARGET_OBJECT_STACK_MEMORY)
+ || (code_cache_enabled_p () && object != TARGET_OBJECT_CODE_MEMORY)))
{
DCACHE *dcache = target_dcache_get ();

@@ -1697,7 +1698,8 @@ target_xfer_partial (struct target_ops *ops,
/* If this is a memory transfer, let the memory-specific code
have a look at it instead. Memory transfers are more
complicated. */
- if (object == TARGET_OBJECT_MEMORY || object == TARGET_OBJECT_STACK_MEMORY)
+ if (object == TARGET_OBJECT_MEMORY || object == TARGET_OBJECT_STACK_MEMORY
+ || object == TARGET_OBJECT_CODE_MEMORY)
retval = memory_xfer_partial (ops, object, readbuf,
writebuf, offset, len);
else
@@ -1799,6 +1801,19 @@ target_read_stack (CORE_ADDR memaddr, gdb_byte *myaddr, ssize_t len)
return TARGET_XFER_E_IO;
}

+/* Like target_read_memory, but specify explicitly that this is a read from
+ the target's code. This may trigger different cache behavior. */
+
+int
+target_read_code (CORE_ADDR memaddr, gdb_byte *myaddr, ssize_t len)
+{
+ if (target_read (current_target.beneath, TARGET_OBJECT_CODE_MEMORY, NULL,
+ myaddr, memaddr, len) == len)
+ return 0;
+ else
+ return TARGET_XFER_E_IO;
+}
+
/* Write LEN bytes from MYADDR to target memory at address MEMADDR.
Returns either 0 for success or a target_xfer_error value if any
error occurs. If an error occurs, no guarantee is made about how
diff --git a/gdb/target.h b/gdb/target.h
index 646907a..890171d 100644
--- a/gdb/target.h
+++ b/gdb/target.h
@@ -145,6 +145,9 @@ enum target_object
if it is not in a region marked as such, since it is known to be
"normal" RAM. */
TARGET_OBJECT_STACK_MEMORY,
+ /* Memory known to be part of the target code. This is cached even
+ if it is not in a region marked as such. */
+ TARGET_OBJECT_CODE_MEMORY,
/* Kernel Unwind Table. See "ia64-tdep.c". */
TARGET_OBJECT_UNWIND_TABLE,
/* Transfer auxilliary vector. */
@@ -1050,6 +1053,8 @@ extern int target_read_memory (CORE_ADDR memaddr, gdb_byte *myaddr,

extern int target_read_stack (CORE_ADDR memaddr, gdb_byte *myaddr, ssize_t len);

+extern int target_read_code (CORE_ADDR memaddr, gdb_byte *myaddr, ssize_t len);
+
extern int target_write_memory (CORE_ADDR memaddr, const gdb_byte *myaddr,
ssize_t len);

--
1.7.7.6