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