[RFC PATCH v1] power: don't manage floating point regs when no FPU

From: Christophe Leroy
Date: Fri Aug 07 2020 - 12:14:08 EST

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There is no point in copying floating point regs when there
is no FPU and MATH_EMULATION is not selected.

Create a new CONFIG_PPC_FPU_REGS bool that is selected by
CONFIG_MATH_EMULATION and CONFIG_PPC_FPU, and use it to
opt out everything related to fp_state in thread_struct.

The following app runs in approx 10.50 seconds on an 8xx without
the patch, and in 9.45 seconds with the patch.

void sigusr1(int sig) { }

int main(int argc, char **argv)
{
int i = 100000;

signal(SIGUSR1, sigusr1);
for (;i--;)
raise(SIGUSR1);
exit(0);
}

Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
---
arch/powerpc/Kconfig | 1 +
arch/powerpc/include/asm/processor.h | 2 ++
arch/powerpc/kernel/asm-offsets.c | 2 ++
arch/powerpc/kernel/process.c | 4 ++++
arch/powerpc/kernel/ptrace/ptrace-novsx.c | 8 ++++++++
arch/powerpc/kernel/ptrace/ptrace.c | 4 ++++
arch/powerpc/kernel/signal.c | 12 +++++++++++-
arch/powerpc/kernel/signal_32.c | 4 ++++
arch/powerpc/kernel/traps.c | 4 ++++
arch/powerpc/platforms/Kconfig.cputype | 4 ++++
10 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 1f48bbfb3ce9..a2611880b904 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -416,6 +416,7 @@ config HUGETLB_PAGE_SIZE_VARIABLE
config MATH_EMULATION
bool "Math emulation"
depends on 4xx || PPC_8xx || PPC_MPC832x || BOOKE
+ select PPC_FPU_REGS
help
Some PowerPC chips designed for embedded applications do not have
a floating-point unit and therefore do not implement the
diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index ed0d633ab5aa..e20b0c5abe62 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -175,8 +175,10 @@ struct thread_struct {
#endif
/* Debug Registers */
struct debug_reg debug;
+#ifdef CONFIG_PPC_FPU_REGS
struct thread_fp_state fp_state;
struct thread_fp_state *fp_save_area;
+#endif
int fpexc_mode; /* floating-point exception mode */
unsigned int align_ctl; /* alignment handling control */
#ifdef CONFIG_HAVE_HW_BREAKPOINT
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 8711c2164b45..6cb36c341c70 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -110,9 +110,11 @@ int main(void)
#ifdef CONFIG_BOOKE
OFFSET(THREAD_NORMSAVES, thread_struct, normsave[0]);
#endif
+#ifdef CONFIG_PPC_FPU
OFFSET(THREAD_FPEXC_MODE, thread_struct, fpexc_mode);
OFFSET(THREAD_FPSTATE, thread_struct, fp_state.fpr);
OFFSET(THREAD_FPSAVEAREA, thread_struct, fp_save_area);
+#endif
OFFSET(FPSTATE_FPSCR, thread_fp_state, fpscr);
OFFSET(THREAD_LOAD_FP, thread_struct, load_fp);
#ifdef CONFIG_ALTIVEC
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 016bd831908e..7e0082ac0a39 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1694,7 +1694,9 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
p->thread.ptrace_bps[i] = NULL;
#endif

+#ifdef CONFIG_PPC_FPU_REGS
p->thread.fp_save_area = NULL;
+#endif
#ifdef CONFIG_ALTIVEC
p->thread.vr_save_area = NULL;
#endif
@@ -1821,8 +1823,10 @@ void start_thread(struct pt_regs *regs, unsigned long start, unsigned long sp)
#endif
current->thread.load_slb = 0;
current->thread.load_fp = 0;
+#ifdef CONFIG_PPC_FPU_REGS
memset(&current->thread.fp_state, 0, sizeof(current->thread.fp_state));
current->thread.fp_save_area = NULL;
+#endif
#ifdef CONFIG_ALTIVEC
memset(&current->thread.vr_state, 0, sizeof(current->thread.vr_state));
current->thread.vr_state.vscr.u[3] = 0x00010000; /* Java mode disabled */
diff --git a/arch/powerpc/kernel/ptrace/ptrace-novsx.c b/arch/powerpc/kernel/ptrace/ptrace-novsx.c
index b2dc4e92d11a..8f87a11f3f8c 100644
--- a/arch/powerpc/kernel/ptrace/ptrace-novsx.c
+++ b/arch/powerpc/kernel/ptrace/ptrace-novsx.c
@@ -21,6 +21,7 @@
int fpr_get(struct task_struct *target, const struct user_regset *regset,
unsigned int pos, unsigned int count, void *kbuf, void __user *ubuf)
{
+#ifdef CONFIG_PPC_FPU_REGS
BUILD_BUG_ON(offsetof(struct thread_fp_state, fpscr) !=
offsetof(struct thread_fp_state, fpr[32]));

@@ -28,6 +29,9 @@ int fpr_get(struct task_struct *target, const struct user_regset *regset,

return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
&target->thread.fp_state, 0, -1);
+#else
+ return 0;
+#endif
}

/*
@@ -47,6 +51,7 @@ int fpr_set(struct task_struct *target, const struct user_regset *regset,
unsigned int pos, unsigned int count,
const void *kbuf, const void __user *ubuf)
{
+#ifdef CONFIG_PPC_FPU_REGS
BUILD_BUG_ON(offsetof(struct thread_fp_state, fpscr) !=
offsetof(struct thread_fp_state, fpr[32]));

@@ -54,4 +59,7 @@ int fpr_set(struct task_struct *target, const struct user_regset *regset,

return user_regset_copyin(&pos, &count, &kbuf, &ubuf,
&target->thread.fp_state, 0, -1);
+#else
+ return 0;
+#endif
}
diff --git a/arch/powerpc/kernel/ptrace/ptrace.c b/arch/powerpc/kernel/ptrace/ptrace.c
index f6e51be47c6e..f162bfec0d3f 100644
--- a/arch/powerpc/kernel/ptrace/ptrace.c
+++ b/arch/powerpc/kernel/ptrace/ptrace.c
@@ -70,6 +70,7 @@ long arch_ptrace(struct task_struct *child, long request,
ret = ptrace_get_reg(child, (int) index, &tmp);
if (ret)
break;
+#ifdef CONFIG_PPC_FPU_REGS
} else {
unsigned int fpidx = index - PT_FPR0;

@@ -79,6 +80,7 @@ long arch_ptrace(struct task_struct *child, long request,
sizeof(long));
else
tmp = child->thread.fp_state.fpscr;
+#endif
}
ret = put_user(tmp, datalp);
break;
@@ -103,6 +105,7 @@ long arch_ptrace(struct task_struct *child, long request,
CHECK_FULL_REGS(child->thread.regs);
if (index < PT_FPR0) {
ret = ptrace_put_reg(child, index, data);
+#ifdef CONFIG_PPC_FPU_REGS
} else {
unsigned int fpidx = index - PT_FPR0;

@@ -113,6 +116,7 @@ long arch_ptrace(struct task_struct *child, long request,
else
child->thread.fp_state.fpscr = data;
ret = 0;
+#endif
}
break;
}
diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c
index d15a98c758b8..18dcbf538f8f 100644
--- a/arch/powerpc/kernel/signal.c
+++ b/arch/powerpc/kernel/signal.c
@@ -133,7 +133,7 @@ unsigned long copy_ckvsx_from_user(struct task_struct *task,
return 0;
}
#endif /* CONFIG_PPC_TRANSACTIONAL_MEM */
-#else
+#elif defined(CONFIG_PPC_FPU_REGS)
inline unsigned long copy_fpr_to_user(void __user *to,
struct task_struct *task)
{
@@ -163,6 +163,16 @@ inline unsigned long copy_ckfpr_from_user(struct task_struct *task,
ELF_NFPREG * sizeof(double));
}
#endif /* CONFIG_PPC_TRANSACTIONAL_MEM */
+#else
+inline unsigned long copy_fpr_to_user(void __user *to, struct task_struct *task)
+{
+ return 0;
+}
+
+inline unsigned long copy_fpr_from_user(struct task_struct *task, void __user *from)
+{
+ return 0;
+}
#endif

/* Log an error when sending an unhandled signal to a process. Controlled
diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
index 96950f189b5a..7b291707eb31 100644
--- a/arch/powerpc/kernel/signal_32.c
+++ b/arch/powerpc/kernel/signal_32.c
@@ -814,7 +814,9 @@ int handle_rt_signal32(struct ksignal *ksig, sigset_t *oldset,
}
regs->link = tramp;

+#ifdef CONFIG_PPC_FPU_REGS
tsk->thread.fp_state.fpscr = 0; /* turn off all fp exceptions */
+#endif

/* create a stack frame for the caller of the handler */
newsp = ((unsigned long)rt_sf) - (__SIGNAL_FRAMESIZE + 16);
@@ -1271,7 +1273,9 @@ int handle_signal32(struct ksignal *ksig, sigset_t *oldset,

regs->link = tramp;

+#ifdef CONFIG_PPC_FPU_REGS
tsk->thread.fp_state.fpscr = 0; /* turn off all fp exceptions */
+#endif

/* create a stack frame for the caller of the handler */
newsp = ((unsigned long)frame) - __SIGNAL_FRAMESIZE;
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index d1ebe152f210..ee9ec61e75b7 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -1188,6 +1188,7 @@ static inline int __parse_fpscr(unsigned long fpscr)
return ret;
}

+#ifdef CONFIG_PPC_FPU
static void parse_fpe(struct pt_regs *regs)
{
int code = 0;
@@ -1198,6 +1199,7 @@ static void parse_fpe(struct pt_regs *regs)

_exception(SIGFPE, regs, code, regs->nip);
}
+#endif

/*
* Illegal instruction emulation support. Originally written to
@@ -1477,11 +1479,13 @@ void program_check_exception(struct pt_regs *regs)
/* We can now get here via a FP Unavailable exception if the core
* has no FPU, in that case the reason flags will be 0 */

+#ifdef CONFIG_PPC_FPU
if (reason & REASON_FP) {
/* IEEE FP exception */
parse_fpe(regs);
goto bail;
}
+#endif
if (reason & REASON_TRAP) {
unsigned long bugaddr;
/* Debugger is first in line to stop recursive faults in
diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index 87737ec86d39..40ffcdba42b8 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -225,9 +225,13 @@ config PPC_E500MC
such as e5500/e6500), and must be disabled for running on
e500v1 or e500v2.

+config PPC_FPU_REGS
+ bool
+
config PPC_FPU
bool
default y if PPC64
+ select PPC_FPU_REGS

config FSL_EMB_PERFMON
bool "Freescale Embedded Perfmon"
--
2.25.0

Next message: Darrick J. Wong: "Re: [RFC PATCH 1/8] fs: introduce get_shared_files() for dax&reflink"
Previous message: Rob Herring: "Re: [PATCH v5 00/14] Add regulator devfreq support to Panfrost"
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