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Replace dcache with splay tree.

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Remove partially implemented writeback support.
	* dcache.c: Include splay-tree.h.
	(LINE_SIZE_POWER): Change from 5 to 6.
	(DCACHE_SIZE): Change from 64 to 4096.
	(ENTRY_INVALID, ENTRY_VALID, ENTRY_DIRTY): Delete.
	(state_chars): Delete.
	(struct dcache_block): Clean up; remove state and anydirty fields.
	(struct dcache_struct): Redefine as a splay tree and linked list.
	(last_cache): Make static.
	(dcache_invalidate, dcache_hit): Rewrite for new cache structure.
	(dcache_read_line, dcache_alloc): Rewrite for new cache structure.
	(dcache_write_line): Delete.
	(dcache_writeback): Delete.
	(dcache_peek_byte): Clean up; remove "invalid" state check.
	(dcache_poke_byte): Rewrite for new cache structure; clarify comment.
	(dcache_splay_tree_compare): New function.
	(dcache_init, dcache_free): Rewrite for new cache structure.
	(dcache_xfer_memory): Rewrite for new write-through cache structure.
	(dcache_print_line): New function.
	(dcache_info): Rewrite for new cache structure.
	(_initialize_dcache): Update "info dcache" help text.
	* dcache.h (dcache_xfer_memory): Update declaration.
	* target.c (memory_xfer_partial): Update calls to dcache_xfer_memory.
This commit is contained in:
Doug Evans 2009-08-20 22:30:12 +00:00
parent 824b28db57
commit 25f122dc09
4 changed files with 275 additions and 333 deletions
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29
gdb/ChangeLog
View file

@ -1,4 +1,31 @@
2009-07-24 Reid Kleckner <reid@kleckner.net>
2009-08-20 Jacob Potter <jdpotter@google.com>
Replace dcache with splay tree.
Remove partially implemented writeback support.
* dcache.c: Include splay-tree.h.
(LINE_SIZE_POWER): Change from 5 to 6.
(DCACHE_SIZE): Change from 64 to 4096.
(ENTRY_INVALID, ENTRY_VALID, ENTRY_DIRTY): Delete.
(state_chars): Delete.
(struct dcache_block): Clean up; remove state and anydirty fields.
(struct dcache_struct): Redefine as a splay tree and linked list.
(last_cache): Make static.
(dcache_invalidate, dcache_hit): Rewrite for new cache structure.
(dcache_read_line, dcache_alloc): Rewrite for new cache structure.
(dcache_write_line): Delete.
(dcache_writeback): Delete.
(dcache_peek_byte): Clean up; remove "invalid" state check.
(dcache_poke_byte): Rewrite for new cache structure; clarify comment.
(dcache_splay_tree_compare): New function.
(dcache_init, dcache_free): Rewrite for new cache structure.
(dcache_xfer_memory): Rewrite for new write-through cache structure.
(dcache_print_line): New function.
(dcache_info): Rewrite for new cache structure.
(_initialize_dcache): Update "info dcache" help text.
* dcache.h (dcache_xfer_memory): Update declaration.
* target.c (memory_xfer_partial): Update calls to dcache_xfer_memory.
2009-08-19 Reid Kleckner <reid@kleckner.net>
Add interface for JIT code generation.
* NEWS: Announce JIT interface.

569
gdb/dcache.c
View file

@ -24,57 +24,34 @@
#include "gdb_string.h"
#include "gdbcore.h"
#include "target.h"
#include "splay-tree.h"
/* The data cache could lead to incorrect results because it doesn't
know about volatile variables, thus making it impossible to debug
functions which use memory mapped I/O devices. Set the nocache
memory region attribute in those cases.
In general the dcache speeds up performance, some speed improvement
In general the dcache speeds up performance. Some speed improvement
comes from the actual caching mechanism, but the major gain is in
the reduction of the remote protocol overhead; instead of reading
or writing a large area of memory in 4 byte requests, the cache
bundles up the requests into 32 byte (actually LINE_SIZE) chunks.
Reducing the overhead to an eighth of what it was. This is very
obvious when displaying a large amount of data,
bundles up the requests into LINE_SIZE chunks, reducing overhead
significantly. This is most useful when accessing a large amount
of data, such as when performing a backtrace.
eg, x/200x 0
The cache is a splay tree along with a linked list for replacement.
Each block caches a LINE_SIZE area of memory. Wtihin each line we remember
the address of the line (which must be a multiple of LINE_SIZE) and the
actual data block.
caching | no yes
----------------------------
first time | 4 sec 2 sec improvement due to chunking
second time | 4 sec 0 sec improvement due to caching
Lines are only allocated as needed, so DCACHE_SIZE really specifies the
*maximum* number of lines in the cache.
The cache structure is unusual, we keep a number of cache blocks
(DCACHE_SIZE) and each one caches a LINE_SIZEed area of memory.
Within each line we remember the address of the line (always a
multiple of the LINE_SIZE) and a vector of bytes over the range.
There's another vector which contains the state of the bytes.
ENTRY_INVALID means that the byte is just plain wrong, and has no
correspondence with anything else (as it would when the cache is
turned on, but nothing has been done to it).
ENTRY_DIRTY means that the byte has some data in it which should be
written out to the remote target one day, but contains correct
data.
ENTRY_VALID means that the data is the same in the cache as it is in
remote memory.
The ENTRY_DIRTY state is necessary because GDB likes to write large
lumps of memory in small bits. If the caching mechanism didn't
maintain the DIRTY information, then something like a two byte
write would mean that the entire cache line would have to be read,
the two bytes modified and then written out again. The alternative
would be to not read in the cache line in the first place, and just
write the two bytes directly into target memory. The trouble with
that is that it really nails performance, because of the remote
protocol overhead. This way, all those little writes are bundled
up into an entire cache line write in one go, without having to
read the cache line in the first place.
*/
At present, the cache is write-through rather than writeback: as soon
as data is written to the cache, it is also immediately written to
the target. Therefore, cache lines are never "dirty". Whether a given
line is valid or not depends on where it is stored in the dcache_struct;
there is no per-block valid flag. */
/* NOTE: Interaction of dcache and memory region attributes
@ -89,20 +66,16 @@
the last bit of the .text segment and the first bit of the .data
segment fall within the same dcache page with a ro/cacheable memory
region defined for the .text segment and a rw/non-cacheable memory
region defined for the .data segment. */
region defined for the .data segment. */
/* This value regulates the number of cache blocks stored.
Smaller values reduce the time spent searching for a cache
line, and reduce memory requirements, but increase the risk
of a line not being in memory */
/* The maximum number of lines stored. The total size of the cache is
equal to DCACHE_SIZE times LINE_SIZE. */
#define DCACHE_SIZE 4096
#define DCACHE_SIZE 64
/* This value regulates the size of a cache line. Smaller values
reduce the time taken to read a single byte, but reduce overall
throughput. */
#define LINE_SIZE_POWER (5)
/* The size of a cache line. Smaller values reduce the time taken to
read a single byte and make the cache more granular, but increase
overhead and reduce the effectiveness of the cache as a prefetcher. */
#define LINE_SIZE_POWER 6
#define LINE_SIZE (1 << LINE_SIZE_POWER)
/* Each cache block holds LINE_SIZE bytes of data
@ -112,59 +85,25 @@
#define XFORM(x) ((x) & LINE_SIZE_MASK)
#define MASK(x) ((x) & ~LINE_SIZE_MASK)
#define ENTRY_INVALID 0 /* data at this byte is wrong */
#define ENTRY_DIRTY 1 /* data at this byte needs to be written back */
#define ENTRY_VALID 2 /* data at this byte is same as in memory */
/* For cache state display by "info dcache".
The letters I,D,V map to
I = ENTRY_INVALID
D = ENTRY_DIRTY
V = ENTRY_VALID */
static const char state_chars[3] = { 'I', 'D', 'V' };
struct dcache_block
{
struct dcache_block *p; /* next in list */
CORE_ADDR addr; /* Address for which data is recorded. */
gdb_byte data[LINE_SIZE]; /* bytes at given address */
unsigned char state[LINE_SIZE]; /* what state the data is in */
/* whether anything in state is dirty - used to speed up the
dirty scan. */
int anydirty;
int refs;
};
/* FIXME: dcache_struct used to have a cache_has_stuff field that was
used to record whether the cache had been accessed. This was used
to invalidate the cache whenever caching was (re-)enabled (if the
cache was disabled and later re-enabled, it could contain stale
data). This was not needed because the cache is write through and
the code that enables, disables, and deletes memory region all
invalidate the cache.
This is overkill, since it also invalidates cache lines from
unrelated regions. One way this could be addressed by adding a
new function that takes an address and a length and invalidates
only those cache lines that match. */
{
struct dcache_block *newer; /* for LRU and free list */
CORE_ADDR addr; /* address of data */
gdb_byte data[LINE_SIZE]; /* bytes at given address */
int refs; /* # hits */
};
struct dcache_struct
{
/* free list */
struct dcache_block *free_head;
struct dcache_block *free_tail;
{
splay_tree tree;
struct dcache_block *oldest;
struct dcache_block *newest;
/* in use list */
struct dcache_block *valid_head;
struct dcache_block *valid_tail;
struct dcache_block *freelist;
/* The cache itself. */
struct dcache_block *the_cache;
};
/* The number of in-use lines in the cache. */
int size;
};
static struct dcache_block *dcache_hit (DCACHE *dcache, CORE_ADDR addr);
@ -174,8 +113,6 @@ static int dcache_read_line (DCACHE *dcache, struct dcache_block *db);
static struct dcache_block *dcache_alloc (DCACHE *dcache, CORE_ADDR addr);
static int dcache_writeback (DCACHE *dcache);
static void dcache_info (char *exp, int tty);
void _initialize_dcache (void);
@ -190,140 +127,54 @@ show_dcache_enabled_p (struct ui_file *file, int from_tty,
}
DCACHE *last_cache; /* Used by info dcache */
static DCACHE *last_cache; /* Used by info dcache */
/* Free all the data cache blocks, thus discarding all cached data. */
void
dcache_invalidate (DCACHE *dcache)
{
int i;
dcache->valid_head = 0;
dcache->valid_tail = 0;
struct dcache_block *block, *next;
dcache->free_head = 0;
dcache->free_tail = 0;
block = dcache->oldest;
for (i = 0; i < DCACHE_SIZE; i++)
while (block)
{
struct dcache_block *db = dcache->the_cache + i;
splay_tree_remove (dcache->tree, (splay_tree_key) block->addr);
next = block->newer;
if (!dcache->free_head)
dcache->free_head = db;
else
dcache->free_tail->p = db;
dcache->free_tail = db;
db->p = 0;
block->newer = dcache->freelist;
dcache->freelist = block;
block = next;
}
return;
dcache->oldest = NULL;
dcache->newest = NULL;
dcache->size = 0;
}
/* If addr is present in the dcache, return the address of the block
containing it. */
containing it. */
static struct dcache_block *
dcache_hit (DCACHE *dcache, CORE_ADDR addr)
{
struct dcache_block *db;
/* Search all cache blocks for one that is at this address. */
db = dcache->valid_head;
splay_tree_node node = splay_tree_lookup (dcache->tree,
(splay_tree_key) MASK (addr));
while (db)
{
if (MASK (addr) == db->addr)
{
db->refs++;
return db;
}
db = db->p;
}
if (!node)
return NULL;
return NULL;
db = (struct dcache_block *) node->value;
db->refs++;
return db;
}
/* Make sure that anything in this line which needs to
be written is. */
/* Fill a cache line from target memory. */
static int
dcache_write_line (DCACHE *dcache, struct dcache_block *db)
{
CORE_ADDR memaddr;
gdb_byte *myaddr;
int len;
int res;
int reg_len;
struct mem_region *region;
if (!db->anydirty)
return 1;
len = LINE_SIZE;
memaddr = db->addr;
myaddr = db->data;
while (len > 0)
{
int s;
int e;
int dirty_len;
region = lookup_mem_region(memaddr);
if (memaddr + len < region->hi)
reg_len = len;
else
reg_len = region->hi - memaddr;
if (!region->attrib.cache || region->attrib.mode == MEM_RO)
{
memaddr += reg_len;
myaddr += reg_len;
len -= reg_len;
continue;
}
while (reg_len > 0)
{
s = XFORM(memaddr);
while (reg_len > 0) {
if (db->state[s] == ENTRY_DIRTY)
break;
s++;
reg_len--;
memaddr++;
myaddr++;
len--;
}
e = s;
while (reg_len > 0) {
if (db->state[e] != ENTRY_DIRTY)
break;
e++;
reg_len--;
}
dirty_len = e - s;
res = target_write (&current_target, TARGET_OBJECT_RAW_MEMORY,
NULL, myaddr, memaddr, dirty_len);
if (res < dirty_len)
return 0;
memset (&db->state[XFORM(memaddr)], ENTRY_VALID, res);
memaddr += res;
myaddr += res;
len -= res;
}
}
db->anydirty = 0;
return 1;
}
/* Read cache line */
static int
dcache_read_line (DCACHE *dcache, struct dcache_block *db)
{
@ -334,26 +185,20 @@ dcache_read_line (DCACHE *dcache, struct dcache_block *db)
int reg_len;
struct mem_region *region;
/* If there are any dirty bytes in the line, it must be written
before a new line can be read */
if (db->anydirty)
{
if (!dcache_write_line (dcache, db))
return 0;
}
len = LINE_SIZE;
memaddr = db->addr;
myaddr = db->data;
while (len > 0)
{
region = lookup_mem_region(memaddr);
if (memaddr + len < region->hi)
/* Don't overrun if this block is right at the end of the region. */
region = lookup_mem_region (memaddr);
if (region->hi == 0 || memaddr + len < region->hi)
reg_len = len;
else
reg_len = region->hi - memaddr;
/* Skip non-cacheable/non-readable regions. */
if (!region->attrib.cache || region->attrib.mode == MEM_WO)
{
memaddr += reg_len;
@ -372,9 +217,6 @@ dcache_read_line (DCACHE *dcache, struct dcache_block *db)
len -= res;
}
memset (db->state, ENTRY_VALID, sizeof (db->data));
db->anydirty = 0;
return 1;
}
@ -386,61 +228,47 @@ dcache_alloc (DCACHE *dcache, CORE_ADDR addr)
{
struct dcache_block *db;
/* Take something from the free list */
db = dcache->free_head;
if (db)
if (dcache->size >= DCACHE_SIZE)
{
dcache->free_head = db->p;
/* Evict the least recently used line. */
db = dcache->oldest;
dcache->oldest = db->newer;
splay_tree_remove (dcache->tree, (splay_tree_key) db->addr);
}
else
{
/* Nothing left on free list, so grab one from the valid list */
db = dcache->valid_head;
db = dcache->freelist;
if (db)
dcache->freelist = db->newer;
else
db = xmalloc (sizeof (struct dcache_block));
if (!dcache_write_line (dcache, db))
return NULL;
dcache->valid_head = db->p;
dcache->size++;
}
db->addr = MASK(addr);
db->addr = MASK (addr);
db->newer = NULL;
db->refs = 0;
db->anydirty = 0;
memset (db->state, ENTRY_INVALID, sizeof (db->data));
/* append this line to end of valid list */
if (!dcache->valid_head)
dcache->valid_head = db;
else
dcache->valid_tail->p = db;
dcache->valid_tail = db;
db->p = 0;
if (dcache->newest)
dcache->newest->newer = db;
dcache->newest = db;
if (!dcache->oldest)
dcache->oldest = db;
splay_tree_insert (dcache->tree, (splay_tree_key) db->addr,
(splay_tree_value) db);
return db;
}
/* Writeback any dirty lines. */
static int
dcache_writeback (DCACHE *dcache)
{
struct dcache_block *db;
db = dcache->valid_head;
while (db)
{
if (!dcache_write_line (dcache, db))
return 0;
db = db->p;
}
return 1;
}
/* Using the data cache DCACHE return the contents of the byte at
address ADDR in the remote machine.
Returns 0 on error. */
Returns 1 for success, 0 for error. */
static int
dcache_peek_byte (DCACHE *dcache, CORE_ADDR addr, gdb_byte *ptr)
@ -450,13 +278,8 @@ dcache_peek_byte (DCACHE *dcache, CORE_ADDR addr, gdb_byte *ptr)
if (!db)
{
db = dcache_alloc (dcache, addr);
if (!db)
return 0;
}
if (db->state[XFORM (addr)] == ENTRY_INVALID)
{
if (!dcache_read_line(dcache, db))
if (!dcache_read_line (dcache, db))
return 0;
}
@ -464,55 +287,78 @@ dcache_peek_byte (DCACHE *dcache, CORE_ADDR addr, gdb_byte *ptr)
return 1;
}
/* Write the byte at PTR into ADDR in the data cache.
Return zero on write error.
*/
The caller is responsible for also promptly writing the data
through to target memory.
If addr is not in cache, this function does nothing; writing to
an area of memory which wasn't present in the cache doesn't cause
it to be loaded in.
Always return 1 to simplify dcache_xfer_memory. */
static int
dcache_poke_byte (DCACHE *dcache, CORE_ADDR addr, gdb_byte *ptr)
{
struct dcache_block *db = dcache_hit (dcache, addr);
if (!db)
{
db = dcache_alloc (dcache, addr);
if (!db)
return 0;
}
if (db)
db->data[XFORM (addr)] = *ptr;
db->data[XFORM (addr)] = *ptr;
db->state[XFORM (addr)] = ENTRY_DIRTY;
db->anydirty = 1;
return 1;
}
static int
dcache_splay_tree_compare (splay_tree_key a, splay_tree_key b)
{
if (a > b)
return 1;
else if (a == b)
return 0;
else
return -1;
}
/* Initialize the data cache. */
DCACHE *
dcache_init (void)
{
int csize = sizeof (struct dcache_block) * DCACHE_SIZE;
DCACHE *dcache;
int i;
dcache = (DCACHE *) xmalloc (sizeof (*dcache));
dcache->the_cache = (struct dcache_block *) xmalloc (csize);
memset (dcache->the_cache, 0, csize);
dcache_invalidate (dcache);
dcache->tree = splay_tree_new (dcache_splay_tree_compare,
NULL,
NULL);
dcache->oldest = NULL;
dcache->newest = NULL;
dcache->freelist = NULL;
dcache->size = 0;
last_cache = dcache;
return dcache;
}
/* Free a data cache */
/* Free a data cache. */
void
dcache_free (DCACHE *dcache)
{
struct dcache_block *db, *next;
if (last_cache == dcache)
last_cache = NULL;
xfree (dcache->the_cache);
splay_tree_delete (dcache->tree);
for (db = dcache->freelist; db != NULL; db = next)
{
next = db->newer;
xfree (db);
}
xfree (dcache);
}
@ -520,66 +366,138 @@ dcache_free (DCACHE *dcache)
to or from debugger address MYADDR. Write to inferior if SHOULD_WRITE is
nonzero.
Returns length of data written or read; 0 for error.
This routine is indended to be called by remote_xfer_ functions. */
Returns length of data written or read; 0 for error. */
int
dcache_xfer_memory (DCACHE *dcache, CORE_ADDR memaddr, gdb_byte *myaddr,
dcache_xfer_memory (struct target_ops *ops, DCACHE *dcache,
CORE_ADDR memaddr, gdb_byte *myaddr,
int len, int should_write)
{
int i;
int res;
int (*xfunc) (DCACHE *dcache, CORE_ADDR addr, gdb_byte *ptr);
xfunc = should_write ? dcache_poke_byte : dcache_peek_byte;
/* Do write-through first, so that if it fails, we don't write to
the cache at all. */
if (should_write)
{
res = target_write (ops, TARGET_OBJECT_RAW_MEMORY,
NULL, myaddr, memaddr, len);
if (res < len)
return 0;
}
for (i = 0; i < len; i++)
{
if (!xfunc (dcache, memaddr + i, myaddr + i))
return 0;
}
/* FIXME: There may be some benefit from moving the cache writeback
to a higher layer, as it could occur after a sequence of smaller
writes have been completed (as when a stack frame is constructed
for an inferior function call). Note that only moving it up one
level to target_xfer_memory() (also target_xfer_memory_partial())
is not sufficent, since we want to coalesce memory transfers that
are "logically" connected but not actually a single call to one
of the memory transfer functions. */
if (should_write)
dcache_writeback (dcache);
return len;
}
/* FIXME: There would be some benefit to making the cache write-back and
moving the writeback operation to a higher layer, as it could occur
after a sequence of smaller writes have been completed (as when a stack
frame is constructed for an inferior function call). Note that only
moving it up one level to target_xfer_memory[_partial]() is not
sufficient since we want to coalesce memory transfers that are
"logically" connected but not actually a single call to one of the
memory transfer functions. */
static void
dcache_print_line (int index)
{
splay_tree_node n;
struct dcache_block *db;
int i, j;
if (!last_cache)
{
printf_filtered (_("No data cache available.\n"));
return;
}
n = splay_tree_min (last_cache->tree);
for (i = index; i > 0; --i)
{
if (!n)
break;
n = splay_tree_successor (last_cache->tree, n->key);
}
if (!n)
{
printf_filtered (_("No such cache line exists.\n"));
return;
}
db = (struct dcache_block *) n->value;
printf_filtered (_("Line %d: address %lx [%d hits]\n"),
index, db->addr, db->refs);
for (j = 0; j < LINE_SIZE; j++)
{
printf_filtered ("%02x ", db->data[j]);
/* Print a newline every 16 bytes (48 characters) */
if ((j % 16 == 15) && (j != LINE_SIZE - 1))
printf_filtered ("\n");
}
printf_filtered ("\n");
}
static void
dcache_info (char *exp, int tty)
{
struct dcache_block *p;
splay_tree_node n;
int i, refcount, lineno;
printf_filtered (_("Dcache line width %d, depth %d\n"),
if (exp)
{
char *linestart;
i = strtol (exp, &linestart, 10);
if (linestart == exp || i < 0)
{
printf_filtered (_("Usage: info dcache [linenumber]\n"));
return;
}
dcache_print_line (i);
return;
}
printf_filtered (_("Dcache line width %d, maximum size %d\n"),
LINE_SIZE, DCACHE_SIZE);
if (last_cache)
if (!last_cache)
{
printf_filtered (_("Cache state:\n"));
for (p = last_cache->valid_head; p; p = p->p)
{
int j;
printf_filtered (_("Line at %s, referenced %d times\n"),
paddress (target_gdbarch, p->addr), p->refs);
for (j = 0; j < LINE_SIZE; j++)
printf_filtered ("%02x", p->data[j] & 0xFF);
printf_filtered (("\n"));
for (j = 0; j < LINE_SIZE; j++)
printf_filtered (" %c", state_chars[p->state[j]]);
printf_filtered ("\n");
}
printf_filtered (_("No data cache available.\n"));
return;
}
refcount = 0;
n = splay_tree_min (last_cache->tree);
i = 0;
while (n)
{
struct dcache_block *db = (struct dcache_block *) n->value;
printf_filtered (_("Line %d: address %lx [%d hits]\n"),
i, db->addr, db->refs);
i++;
refcount += db->refs;
n = splay_tree_successor (last_cache->tree, n->key);
}
printf_filtered (_("Cache state: %d active lines, %d hits\n"), i, refcount);
}
void
@ -601,8 +519,7 @@ volatile registers are in use. By default, this option is off."),
add_info ("dcache", dcache_info,
_("\
Print information on the dcache performance.\n\
The state of each cached byte is represented by a letter:\n\
I = invalid\n\
D = dirty\n\
V = valid"));
With no arguments, this command prints the cache configuration and a\n\
summary of each line in the cache. Use \"info dcache <lineno> to dump\"\n\
the contents of a given line."));
}

4
gdb/dcache.h
View file

@ -35,7 +35,7 @@ void dcache_free (DCACHE *);
/* Simple to call from <remote>_xfer_memory */
int dcache_xfer_memory (DCACHE *cache, CORE_ADDR mem, gdb_byte *my,
int len, int should_write);
int dcache_xfer_memory (struct target_ops *ops, DCACHE *cache, CORE_ADDR mem,
gdb_byte *my, int len, int should_write);
#endif /* DCACHE_H */

6
gdb/target.c
View file

@ -1225,16 +1225,14 @@ memory_xfer_partial (struct target_ops *ops, void *readbuf, const void *writebuf
if (region->attrib.cache)
{
/* FIXME drow/2006-08-09: This call discards OPS, so the raw
memory request will start back at current_target. */
if (readbuf != NULL)
res = dcache_xfer_memory (target_dcache, memaddr, readbuf,
res = dcache_xfer_memory (ops, target_dcache, memaddr, readbuf,
reg_len, 0);
else
/* FIXME drow/2006-08-09: If we're going to preserve const
correctness dcache_xfer_memory should take readbuf and
writebuf. */
res = dcache_xfer_memory (target_dcache, memaddr,
res = dcache_xfer_memory (ops, target_dcache, memaddr,
(void *) writebuf,
reg_len, 1);
if (res <= 0)