lib: improve the performance of memcpy and memmove of the general version

the performance of memcpy and memmove of the general version is very inefficient, this patch improved them.

---
 lib/string.c |   32 ++++++++++++++------------------
 1 files changed, 14 insertions(+), 18 deletions(-)

index f71bead..6cbf6d8 100644
@@ -23,6 +23,7 @@
 #include <linux/string.h>
 #include <linux/ctype.h>
 #include <linux/module.h>
+#include <linux/memcopy.h>
 
 #ifndef __HAVE_ARCH_STRNICMP
 /**

@@ -567,11 +568,12 @@ EXPORT_SYMBOL(memset);
  */
 void *memcpy(void *dest, const void *src, size_t count)
 {
-	char *tmp = dest;
-	const char *s = src;
+	unsigned long dstp = (unsigned long)dest;
+	unsigned long srcp = (unsigned long)src;
+
+	/* Copy from the beginning to the end */
+	mem_copy_fwd(dstp, srcp, count);
 
-	while (count--)
-		*tmp++ = *s++;
 	return dest;
 }
 EXPORT_SYMBOL(memcpy);

@@ -588,21 +590,15 @@ EXPORT_SYMBOL(memcpy);
  */
 void *memmove(void *dest, const void *src, size_t count)
 {
-	char *tmp;
-	const char *s;
-
-	if (dest <= src) {
-		tmp = dest;
-		s = src;
-		while (count--)
-			*tmp++ = *s++;
+	unsigned long dstp = (unsigned long)dest;
+	unsigned long srcp = (unsigned long)src;
+
+	if (dest - src >= count) {
+		/* Copy from the beginning to the end */
+		mem_copy_fwd(dstp, srcp, count);
 	} else {
-		tmp = dest;
-		tmp += count;
-		s = src;
-		s += count;
-		while (count--)
-			*--tmp = *--s;
+		/* Copy from the end to the beginning */
+		mem_copy_bwd(dstp, srcp, count);
 	}
 	return dest;
 }

1.7.0.1

* Miao Xie:

I think you need to change that to EXPORT_SYMBOL_GPL, because the code is now licensed under the GPL, and not the GPL plus kernel exceptions (whatever they are, but they undoubtly exist), unlike the original implementation.

--=20
=46lorian Weimer <[email protected]>
BFK edv-consulting GmbH http://www.bfk.de/
Kriegsstra=DFe 100 tel: +49-721-96201-1
D-76133 Karlsruhe fax: +49-721-96201-99

Ouch. That would basically make it impossible to implement a non-GPL module. Also, this should only apply to the "lib" version of the memcpy() routine, not the arch-specific ones that are written in assembly (maybe that already is true, I'm not sure).

Lustre is GPL, so it isn't fatal for us, but it definitely seems draconian, and almost a reason not to include this patch into the kernel. Also, given that the original code is LGPL (which allows linking to non-GPL code) this seems counter to the intent of the original authors.

I suspect there isn't anything so brilliant in the glibc memcpy() that it couldn't be re-implemented without copying the code. "implement memcpy with aligned machine-word-sized chunks" would be enough for anyone to reimplement it without ever having come close to the glibc code.

Cheers, Andreas

I wouldn't think so - the intent of EXPORT_SYMBOL_GPL is to mark symbols that make it obvious that a module was derived from the Linux kernel, as opposed to some sort of generic driver that was just ported to a new interface. (It's not foolproof, it's more of a warning to developers.)

If you think of it this way, memcpy is a function defined in the C standard, there's absolutely nothing Linux-specific about using it.

Of course, IANAL; and you should probably grab some more opinions on the matter.

Calvin Walton <[email protected]>

EXPORT_SYMBOL_GPL was meant for symbols that were clearly internal workings. EXPORT_SYMBOL() doesn't in any way imply or excuse GPL compliance for any derivative work.

Using the FSF memcpy seems a good technical idea, and it'll no doubt liven up the proprietary module makers lawyers as it'll make the FSF a party to any infringement disputes 8)

Alan