A new patch for hint_pause

I (finally) applied the attached patch for 2.4. It's slightly different than what you sent me because I reworked the processor.h changes slightly to reduce the diff with 2.5.

I don't think this patch went to linux-ia64 originally, so I'm copying it just as a heads-up. (And to encourage people to copy the list so we have a convenient archive).

Bjorn

#### AUTHOR [email protected]
#### COMMENT START
### Comments for ChangeSet
ia64: use "hint @pause" in cpu_relax() and spinlock contention.
### Comments for arch/ia64/scripts/make_gas_hint_test.c
Test case to determine whether gas supports "hint @pause".
### Comments for arch/ia64/scripts/make_gas_hint_test.c
BitKeeper file /home/helgaas/linux/testing/arch/ia64/scripts/make_gas_hint_test.c ### Comments for arch/ia64/Makefile
Check for binutils support of "hint @pause" and use -DGAS_HAS_HINT_INSN appropriately. ### Comments for arch/ia64/kernel/head.S
(ia64_spinlock_contention): Use "hint @pause".
### Comments for include/asm-ia64/processor.h
(cpu_relax): Use "hint @pause".
### Comments for include/asm-ia64/spinlock.h
(spin_lock, read_lock, write_lock): Use "hint @pause".
#### COMMENT END

# This is a BitKeeper generated patch for the following project:
# Project Name: Linux kernel tree
# This patch format is intended for GNU patch command version 2.5 or higher. # This patch includes the following deltas:
# ChangeSet 1.1043 -> 1.1044
# arch/ia64/Makefile 1.9 -> 1.10
# include/asm-ia64/spinlock.h 1.6 -> 1.7
# include/asm-ia64/processor.h 1.20 -> 1.21
# arch/ia64/kernel/head.S 1.9 -> 1.10
# (new) -> 1.1 arch/ia64/scripts/make_gas_hint_test.c
#
# The following is the BitKeeper ChangeSet Log
# --------------------------------------------
# 03/07/29 [email protected] 1.1044

# hint
# --------------------------------------------
#
diff -Nru a/arch/ia64/Makefile b/arch/ia64/Makefile
--- a/arch/ia64/Makefile	Tue Jul 29 17:18:01 2003
+++ b/arch/ia64/Makefile	Tue Jul 29 17:18:01 2003
@@ -24,6 +24,23 @@

GCC_VERSION=$(shell $(CC) -v 2>&1 | fgrep 'gcc version' | cut -f3 -d' ' | cut -f1 -d'.')

+CHECK_GAS_FOR_HINT=arch/ia64/scripts/check_gas_for_hint.o
+MAKE_GAS_HINT_TEST=arch/ia64/scripts/make_gas_hint_test
+
+ifneq (, $(shell ls $(CHECK_GAS_FOR_HINT)))
+$(shell rm $(CHECK_GAS_FOR_HINT))
+endif
+
+CHECK_GAS_CMD:=($(CC) $(MAKE_GAS_HINT_TEST).c -o $(MAKE_GAS_HINT_TEST) |$(AS) -o $(CHECK_GAS_FOR_HINT) -;rm $(MAKE_GAS_HINT_TEST))>&/dev/null +$(shell $(CHECK_GAS_CMD))
+ifneq (, $(shell ls $(CHECK_GAS_FOR_HINT)))
+#Newer version of binutil is detected and "hint" instruction is in the kernel
+FLAGS := $(AFLAGS) -DGAS_HAS_HINT_INSN
+CFLAGS := $(CFLAGS) -DGAS_HAS_HINT_INSN
+else
+$(warning Warning: Please use binutil version 2.14.90.0.4.1 or higher to get the support of hint instruction in kernel.) +endif
+
ifneq ($(GCC_VERSION),2)
CFLAGS += -frename-registers --param max-inline-insnsP00
endif

diff -Nru a/arch/ia64/kernel/head.S b/arch/ia64/kernel/head.S
@@ -782,6 +782,9 @@
 	;;
 	// delay a little...
 .wait:	sub tmp=tmp,timeout
+#ifdef GAS_HAS_HINT_INSN
+	hint @pause
+#endif
 	or delay=0xf,delay	// make sure delay is non-zero (otherwise we get stuck with 0)
 	;;
 	cmp.lt p15,p0=tmp,r0

diff -Nru a/arch/ia64/scripts/make_gas_hint_test.c b/arch/ia64/scripts/make_gas_hint_test.c
@@ -0,0 +1,15 @@
+// The code generates a test case which is used
+// to detect whether Binutil supports hint
+// instruction correctly or not.
+#include <string.h>
+#include <stdio.h>
+
+int main()
+{
+	char str[32766];
+	memset(str,'\n',32765);
+	str[32765]=0;
+	printf("%s(p7) hint @pause\n",str);
+
+	return 0;
+}

diff -Nru a/include/asm-ia64/processor.h b/include/asm-ia64/processor.h
@@ -656,8 +656,18 @@
 	asm volatile ("mov cr.lrr0=%0;; srlz.d" :: "r"(val) : "memory");
 }
 
-#define cpu_relax()	do { } while (0)
+#ifdef GAS_HAS_HINT_INSN
+static inline void
+ia64_hint_pause (void)
+{
+	asm volatile ("hint @pause" ::: "memory");
+}
 
+#else
+#define ia64_hint_pause()	do { } while (0)
+#endif
+
+#define cpu_relax()	ia64_hint_pause()
 
 static inline void
 ia64_set_lrr1 (unsigned long val)

diff -Nru a/include/asm-ia64/spinlock.h b/include/asm-ia64/spinlock.h
@@ -74,6 +74,12 @@
 #define SPIN_LOCK_UNLOCKED			(spinlock_t) { 0 }
 #define spin_lock_init(x)			((x)->lock = 0)
 
+#ifdef GAS_HAS_HINT_INSN
+#define HINT_PAUSE	";; (p7) hint @pause\n"
+#else
+#define HINT_PAUSE
+#endif										
+
 /*
  * Streamlined test_and_set_bit(0, (x)).  We use test-and-test-and-set
  * rather than a simple xchg to avoid writing the cache-line when

@@ -87,6 +93,7 @@
 	"ld4 r2 = [%0]\n"					\
 	";;\n"							\
 	"cmp4.eq p0,p7 = r0,r2\n"				\
+	HINT_PAUSE 						\
 	"(p7) br.cond.spnt.few 1b \n"				\
 	"cmpxchg4.acq r2 = [%0], r29, ar.ccv\n"			\
 	";;\n"							\

@@ -115,20 +122,21 @@
 	int tmp = 0;								\
 	__asm__ __volatile__ ("1:\tfetchadd4.acq %0 = [%1], 1\n"		\
 			      ";;\n"						\
-			      "tbit.nz p6,p0 = %0, 31\n"			\
-			      "(p6) br.cond.sptk.few 2f\n"			\
+			      "tbit.nz p7,p0 = %0, 31\n"			\
+			      "(p7) br.cond.sptk.few 2f\n"			\
 			      ".section .text.lock,\"ax\"\n"			\
 			      "2:\tfetchadd4.rel %0 = [%1], -1\n"		\
 			      ";;\n"						\
 			      "3:\tld4.acq %0 = [%1]\n"				\
 			      ";;\n"						\
-			      "tbit.nz p6,p0 = %0, 31\n"			\
-			      "(p6) br.cond.sptk.few 3b\n"			\
+			      "tbit.nz p7,p0 = %0, 31\n"			\
+			      HINT_PAUSE					\
+			      "(p7) br.cond.sptk.few 3b\n"			\
 			      "br.cond.sptk.few 1b\n"				\
 			      ";;\n"						\
 			      ".previous\n"					\
 			      : "=&r" (tmp)					\
-			      : "r" (rw) : "p6", "memory");			\
+			      : "r" (rw) : "p7", "memory");			\
 } while(0)
 
 #define read_unlock(rw)								\

@@ -150,6 +158,7 @@
 		"ld4 r2 = [%0]\n"						\
 		";;\n"								\
 		"cmp4.eq p0,p7 = r0,r2\n"					\
+		HINT_PAUSE							\
 		"(p7) br.cond.spnt.few 1b \n"					\
 		"cmpxchg4.acq r2 = [%0], r29, ar.ccv\n"				\
 		";;\n"								\

Making a new binutils a requirement would be considered too drastic?

--cw

It is a requirement if the kernel wants to have the hint_pause instruction. If the right version of binutil is not installed then kernel will be built without this support.

rohit

So all of this is in the latest CVS version of binutils? Any idea when a release version will support the new features?

Thanks,
Jesse

I released the Linux binutils 2.14.90.0.4.1 on 06/24/2003 and the current one is 2.14.90.0.5 which was released on 07/22/2003.

H.J.

I see them now--at the redhat site, earlier I was looking at gnu.org.

Thanks,
Jesse

Err, I meant kernel.org. I'll give this release a try.

Thanks,
Jesse

FYI, the Linux binutils is available at

http://www.kernel.org/pub/linux/devel/binutils/

H.J.

I think the new binutils is a requirement for 2.5/2.6, but I didn't want to force that for 2.4.

Bjorn