Re: Testing 7.0 Beta: FFS still very slow when creating files

["J. Hannken-Illjes" <hannken%eis.cs.tu-bs.de@localhost>]

On 25 Aug 2014, at 15:55, J. Hannken-Illjes <hannken%eis.cs.tu-bs.de@localhost> 
wrote:

> On 24 Aug 2014, at 18:57, J. Hannken-Illjes 
> <hannken%eis.cs.tu-bs.de@localhost> wrote:
> 
> <snip>
> 
>> I tried to bisect and got an increase in time from ~15 secs to ~24 secs
>> between the time stamps '2012-09-18 06:00 UTC' '2012-09-18 09:00 UTC'.
>> 
>> Someone should redo this test as this interval is the import of the
>> compiler (GCC 4.5.3 -> 4.5.4) and I had to rebuild tools.  I cant
>> believe this to be a compiler problem.
> 
> GCC 4.5.4 disabled builtin memcmp as x86 has no cmpmemsi pattern.
> 
> See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43052, Comment 16.
> 
> Could this be the cause of this big loss in performance?

Short answer: it is -- reverting external/gpl3/gcc/dist/gcc/builtins.c
from Rev. 1.3 to 1.2 brings back the old times which are the same as
they were on NetBSD 6.

Given that this test has many calls to ufs_lookup/cache_lookup using
memcmp to check for equal filenames this is not a surprise.

A rather naive "implementation" of memcmp (see below) drops the running
time from ~15 sec to ~9 secs.  We should consider improving our memcmp.

--
J. Hannken-Illjes - hannken%eis.cs.tu-bs.de@localhost - TU Braunschweig 
(Germany)

Index: libkern.h
===================================================================
RCS file: /cvsroot/src/sys/lib/libkern/libkern.h,v
retrieving revision 1.106
diff -p -u -2 -r1.106 libkern.h
--- libkern.h   30 Aug 2012 12:16:49 -0000      1.106
+++ libkern.h   25 Aug 2014 17:23:35 -0000
@@ -262,5 +262,18 @@ void       *memset(void *, int, size_t);
 #if __GNUC_PREREQ__(2, 95) && !defined(_STANDALONE)
 #define        memcpy(d, s, l)         __builtin_memcpy(d, s, l)
-#define        memcmp(a, b, l)         __builtin_memcmp(a, b, l)
+static inline int __memcmp(const void *a, const void *b, size_t l)
+{
+       const unsigned char *pa = a, *pb = b;
+
+       if (l > 8)
+               return memcmp(a, b, l);
+       while (l-- > 0) {
+               if (__predict_false(*pa != *pb))
+                       return *pa < *pb ? -1 : 1;
+               pa++; pb++;
+       }
+       return 0;
+}
+#define        memcmp(a, b, l)         __memcmp(a, b, l)
 #endif
 #if __GNUC_PREREQ__(2, 95) && !defined(_STANDALONE)