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ieee754_csr is the problem (Re: lazy fpu switch irrelavant to no-fpu ca

To: linux-mips@oss.sgi.com
Subject: ieee754_csr is the problem (Re: lazy fpu switch irrelavant to no-fpu case?
From: Jun Sun <jsun@mvista.com>
Date: Thu, 21 Feb 2002 19:57:16 -0800
References: <3C75B181.C5A065A1@mvista.com>
Sender: owner-linux-mips@oss.sgi.com
Jun Sun wrote:
> Anyhow, the problem I am seeing with FPU/SMP case seems to be caused by FPU
> emulation code itself, if we can assume it is not caused by fpu context
> switch.  Right now the FPU is not turned on on the box.
> 

OK, I found the guilt part in FPU emul.  It is the global variable
ieee754_csr.  The following patch seems to fix the problem.  I am sure someone
who are more familiar with FPU might be able to make it more elegant.

There is another global variable which is potentially dangerous for SMP.  It
is fpuemuprivate.  Currently it is used in almost used for accounting and
read-only purpose.  I did not bother to change it.  It should be fixed too, I
suppose.

Cheers.

Jun
diff -Nru linux/arch/mips/math-emu/ieee754.h.orig 
linux/arch/mips/math-emu/ieee754.h
--- linux/arch/mips/math-emu/ieee754.h.orig     Thu Jan 31 17:13:26 2002
+++ linux/arch/mips/math-emu/ieee754.h  Thu Feb 21 19:34:06 2002
@@ -323,7 +323,7 @@
 
 /* the control status register 
 */
-struct ieee754_csr {
+struct ieee754_csr_struct {
        unsigned pad:13;
        unsigned nod:1;         /* set 1 for no denormalised numbers */
        unsigned cx:5;          /* exceptions this operation */
@@ -331,7 +331,13 @@
        unsigned sx:5;          /* exceptions total */
        unsigned rm:2;          /* current rounding mode */
 };
-extern struct ieee754_csr ieee754_csr;
+
+#include <linux/sched.h>
+#include <linux/threads.h>
+#include <linux/smp.h>
+#include <asm/current.h>
+extern struct ieee754_csr_struct ieee754_csr_array[NR_CPUS];
+#define        ieee754_csr ieee754_csr_array[smp_processor_id()]
 
 static __inline unsigned ieee754_getrm(void)
 {
diff -Nru linux/arch/mips/math-emu/ieee754.c.orig 
linux/arch/mips/math-emu/ieee754.c
--- linux/arch/mips/math-emu/ieee754.c.orig     Mon Jan 28 11:17:14 2002
+++ linux/arch/mips/math-emu/ieee754.c  Thu Feb 21 19:37:32 2002
@@ -52,7 +52,7 @@
 
 /* the control status register 
 */
-struct ieee754_csr ieee754_csr;
+struct ieee754_csr_struct ieee754_csr_array[NR_CPUS];
 
 /* special constants
 */
diff -Nru linux/arch/mips/math-emu/cp1emu.c.orig 
linux/arch/mips/math-emu/cp1emu.c
--- linux/arch/mips/math-emu/cp1emu.c.orig      Mon Jan 28 11:17:14 2002
+++ linux/arch/mips/math-emu/cp1emu.c   Thu Feb 21 19:22:45 2002
@@ -945,7 +945,7 @@
 static ieee754##p fpemu_##p##_##name (ieee754##p r, ieee754##p s, \
     ieee754##p t) \
 { \
-    struct ieee754_csr ieee754_csr_save; \
+    struct ieee754_csr_struct ieee754_csr_save; \
     s = f1 (s, t); \
     ieee754_csr_save = ieee754_csr; \
     s = f2 (s, r); \
diff -Nru linux/arch/mips/math-emu/dp_sqrt.c.orig 
linux/arch/mips/math-emu/dp_sqrt.c
--- linux/arch/mips/math-emu/dp_sqrt.c.orig     Thu Feb 21 19:41:09 2002
+++ linux/arch/mips/math-emu/dp_sqrt.c  Thu Feb 21 19:39:08 2002
@@ -37,7 +37,7 @@
 
 ieee754dp ieee754dp_sqrt(ieee754dp x)
 {
-       struct ieee754_csr oldcsr;
+       struct ieee754_csr_struct oldcsr;
        ieee754dp y, z, t;
        unsigned scalx, yh;
        COMPXDP;
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