Re: [PATCH] alpha dl-machine.h fix (take 2)

[Richard Henderson <rth at twiddle dot net>]

On Fri, Aug 31, 2001 at 06:41:28PM +0200, Jakub Jelinek wrote:
> 	* sysdeps/alpha/dl-machine.h (elf_machine_rela): Remove unused code.
> 	Don't add old memory content for R_ALPHA_REFQUAD.

This is ok.  I tested this plus variants that

  (1) Used __builtin_expect to avoid memcpy for the unaligned cases, and
  (2) Added a prefetch-with-write-intent against the relocation address
      at the top of the function.

The result appears to be that these changes are in the noise.

I used the following hack to get cycle counts from ld.so.  It'd be
nice if they could go in, but I could easily imagine Uli barfing.


r~


Relocation performance summary:

		ls		cvs		emacs		aspell

relocs:		936		2431		4319		5431

cycles:

OLD-ALIGN	-17429		-120315		-260707		 -90156
		 33515		 180431		 211068		-521220
		-15865		  58516		  41576		-249110

OLD-PREFETCH	-42554		   1691		-118651		-250081
		 79639		 142492		  47157		  98095
		-41410		 -62520		  93174		   -160

ALIGN-PREFETCH	-25125		 122006		 142056		-159925
		 46124		 -37939		-163911		 619315
		-25545		-121036		  51598		 248950

percent time:

OLD-ALIGN	 0.3		 0.0		 0.0		-0.3
		-1.6		 0.3		 0.1		 0.0
		 1.1		 0.0		 0.1		-0.1

OLD-PREFETCH	-0.1		 0.3		-0.1		 0.0
		-2.4		-0.2		-0.2		-0.1
		 1.2		 0.0		 0.0		 0.0




	* elf/dl-support.c (_dl_cpuclock_offset): Protect with NONAVAIL.
	(HP_TIMING_AVAIL): Set to HP_SMALL_TIMING_AVAIL if present.
	* elf/rtld.c (HP_TIMING_AVAIL): Likewise.
	(print_statistics): Make scalar unsigned long long.
	* sysdeps/alpha/hp-timing.h: New file.

Index: elf/dl-support.c
===================================================================
RCS file: /cvs/glibc/libc/elf/dl-support.c,v
retrieving revision 1.52
diff -u -r1.52 dl-support.c
--- dl-support.c	2001/07/27 03:48:11	1.52
+++ dl-support.c	2001/09/01 01:12:32
@@ -93,8 +93,14 @@
 /* Nonzero during startup.  */
 int _dl_starting_up = 1;
 
+/* We expect less than a second for relocation.  */
+#ifdef HP_SMALL_TIMING_AVAIL 
+#undef HP_TIMING_AVAIL
+#define HP_TIMING_AVAIL HP_SMALL_TIMING_AVAIL
+#endif
+
 /* Initial value of the CPU clock.  */
-#if HP_TIMING_AVAIL
+#ifndef HP_TIMING_NONAVAIL
 hp_timing_t _dl_cpuclock_offset;
 #endif
 
@@ -133,9 +139,8 @@
 static void
 non_dynamic_init (void)
 {
-#if HP_TIMING_AVAIL
-  HP_TIMING_NOW (_dl_cpuclock_offset);
-#endif
+  if (HP_TIMING_AVAIL)
+    HP_TIMING_NOW (_dl_cpuclock_offset);
 
   if (!_dl_pagesize)
     _dl_pagesize = __getpagesize ();
Index: elf/rtld.c
===================================================================
RCS file: /cvs/glibc/libc/elf/rtld.c,v
retrieving revision 1.207
diff -u -r1.207 rtld.c
--- rtld.c	2001/08/27 16:21:32	1.207
+++ rtld.c	2001/09/01 01:12:33
@@ -121,6 +121,12 @@
 struct libname_list _dl_rtld_libname;
 struct libname_list _dl_rtld_libname2;
 
+/* We expect less than a second for relocation.  */
+#ifdef HP_SMALL_TIMING_AVAIL
+#undef HP_TIMING_AVAIL
+#define HP_TIMING_AVAIL HP_SMALL_TIMING_AVAIL
+#endif
+
 /* Variable for statistics.  */
 #ifndef HP_TIMING_NONAVAIL
 static hp_timing_t rtld_total_time;
@@ -1506,7 +1512,7 @@
     {
       char pbuf[30];
       HP_TIMING_PRINT (buf, sizeof (buf), relocate_time);
-      cp = _itoa_word ((1000 * relocate_time) / rtld_total_time,
+      cp = _itoa_word ((1000ULL * relocate_time) / rtld_total_time,
 		       pbuf + sizeof (pbuf), 10, 0);
       wp = pbuf;
       switch (pbuf + sizeof (pbuf) - cp)
@@ -1535,7 +1541,7 @@
     {
       char pbuf[30];
       HP_TIMING_PRINT (buf, sizeof (buf), load_time);
-      cp = _itoa_word ((1000 * load_time) / rtld_total_time,
+      cp = _itoa_word ((1000ULL * load_time) / rtld_total_time,
 		       pbuf + sizeof (pbuf), 10, 0);
       wp = pbuf;
       switch (pbuf + sizeof (pbuf) - cp)
--- /dev/null	Thu Oct 19 13:35:05 2000
+++ sysdeps/alpha/hp-timing.h	Fri Aug 31 18:18:02 2001
@@ -0,0 +1,118 @@
+/* High precision, low overhead timing functions.  IA-64 version.
+   Copyright (C) 2001 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Richard Henderson <rth@redhat.com>, 2001.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+#ifndef _HP_TIMING_H
+#define _HP_TIMING_H	1
+
+#include <string.h>
+#include <sys/param.h>
+#include <stdio-common/_itoa.h>
+
+/* The macros defined here use the timestamp counter in IA-64.  They
+   provide a very accurate way to measure the time with very little
+   overhead.  The time values themself have no real meaning, only
+   differences are interesting.
+
+   The list of macros we need includes the following:
+
+   - HP_TIMING_AVAIL: test for availability.
+
+   - HP_TIMING_INLINE: this macro is non-zero if the functionality is not
+     implemented using function calls but instead uses some inlined code
+     which might simply consist of a few assembler instructions.  We have to
+     know this since we might want to use the macros here in places where we
+     cannot make function calls.
+
+   - hp_timing_t: This is the type for variables used to store the time
+     values.
+
+   - HP_TIMING_ZERO: clear `hp_timing_t' object.
+
+   - HP_TIMING_NOW: place timestamp for current time in variable given as
+     parameter.
+
+   - HP_TIMING_DIFF_INIT: do whatever is necessary to be able to use the
+     HP_TIMING_DIFF macro.
+
+   - HP_TIMING_DIFF: compute difference between two times and store it
+     in a third.  Source and destination might overlap.
+
+   - HP_TIMING_ACCUM: add time difference to another variable.  This might
+     be a bit more complicated to implement for some platforms as the
+     operation should be thread-safe and 64bit arithmetic on 32bit platforms
+     is not.
+
+   - HP_TIMING_ACCUM_NT: this is the variant for situations where we know
+     there are no threads involved.
+
+   - HP_TIMING_PRINT: write decimal representation of the timing value into
+     the given string.  This operation need not be inline even though
+     HP_TIMING_INLINE is specified.
+*/
+
+/* We always have the timestamp register, but it's got only a 4 second
+   range.  Use it for ld.so profiling only.  */
+#define HP_TIMING_AVAIL		(0)
+#define HP_SMALL_TIMING_AVAIL	(1)
+
+/* We indeed have inlined functions.  */
+#define HP_TIMING_INLINE	(1)
+
+/* We use 32 bit values for the times.  */
+typedef unsigned int hp_timing_t;
+
+/* Set timestamp value to zero.  */
+#define HP_TIMING_ZERO(VAR)	(VAR) = (0)
+
+/* The "rpcc" instruction returns a 32-bit counting half and a 32-bit
+   "virtual cycle counter displacement".  Subtracting the two gives us
+   a virtual cycle count.  */
+#define HP_TIMING_NOW(VAR)			\
+  do {						\
+    unsigned long x_;				\
+    asm volatile ("rpcc %0" : "=r"(x_));	\
+    (VAR) = (int)(x_) - (int)(x_ >> 32);	\
+  } while (0)
+
+/* ??? Two rpcc instructions can be scheduled simultaneously.  */
+#define HP_TIMING_DIFF_INIT() do { } while (0)
+
+/* It's simple arithmetic for us.  */
+#define HP_TIMING_DIFF(Diff, Start, End)	(Diff) = ((End) - (Start))
+
+/* ??? Don't bother, since we're only used for ld.so.  */
+#define HP_TIMING_ACCUM(Sum, Diff)  not implemented
+
+/* No threads, no extra work.  */
+#define HP_TIMING_ACCUM_NT(Sum, Diff)	(Sum) += (Diff)
+
+/* Print the time value.  */
+#define HP_TIMING_PRINT(Buf, Len, Val) \
+  do {									      \
+    char __buf[20];							      \
+    char *__cp = _itoa_word (Val, __buf + sizeof (__buf), 10, 0);	      \
+    int __len = (Len);							      \
+    char *__dest = (Buf);						      \
+    while (__len-- > 0 && __cp < __buf + sizeof (__buf))		      \
+      *__dest++ = *__cp++;						      \
+    memcpy (__dest, " clock cycles", MIN (__len, sizeof (" clock cycles")));  \
+  } while (0)
+
+#endif	/* hp-timing.h */