Re: [PATCH v5] powerpc/irq: inline call_do_irq() and call_do_softirq() on PPC32

[Christophe Leroy]

Hi Michael,

Le 07/12/2019 à 18:20, Christophe Leroy a écrit :

call_do_irq() and call_do_softirq() are simple enough to be
worth inlining.

Inlining them avoids an mflr/mtlr pair plus a save/reload on stack.
It also allows GCC to keep the saved ksp_limit in an nonvolatile reg.

This is inspired from S390 arch. Several other arches do more or
less the same. The way sparc arch does seems odd thought.

Signed-off-by: Christophe Leroy <christophe.le...@c-s.fr>
Reviewed-by: Segher Boessenkool <seg...@kernel.crashing.org>

Anything more I need to do for this patch to get merged ?

Thanks
Christophe

---
v2: no change.
v3: no change.
v4:
- comment reminding the purpose of the inline asm block.
- added r2 as clobbered reg
v5:
- Limiting the change to PPC32 for now.
- removed r2 from the clobbered regs list (on PPC32 r2 points to current all 
the time)
- Removed patch 1 and merged ksp_limit handling in here.
---
  arch/powerpc/include/asm/irq.h |  2 ++
  arch/powerpc/kernel/irq.c      | 48 ++++++++++++++++++++++++++++++++++++++++++
  arch/powerpc/kernel/misc_32.S  | 39 ----------------------------------
  3 files changed, 50 insertions(+), 39 deletions(-)

diff --git a/arch/powerpc/include/asm/irq.h b/arch/powerpc/include/asm/irq.h
index 814dfab7e392..e4a92f0b4ad4 100644
--- a/arch/powerpc/include/asm/irq.h
+++ b/arch/powerpc/include/asm/irq.h
@@ -56,8 +56,10 @@ extern void *mcheckirq_ctx[NR_CPUS];
  extern void *hardirq_ctx[NR_CPUS];
  extern void *softirq_ctx[NR_CPUS];

+#ifdef CONFIG_PPC64

  void call_do_softirq(void *sp);
  void call_do_irq(struct pt_regs *regs, void *sp);
+#endif
  extern void do_IRQ(struct pt_regs *regs);
  extern void __init init_IRQ(void);
  extern void __do_irq(struct pt_regs *regs);
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index 5645bc9cbc09..240eca12c71d 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -611,6 +611,54 @@ static inline void check_stack_overflow(void)
  #endif
  }

+#ifdef CONFIG_PPC32

+static inline void call_do_softirq(const void *sp)
+{
+       register unsigned long ret asm("r3");
+       unsigned long limit = current->thread.ksp_limit;
+
+       /* Adjust the stack limit */
+       current->thread.ksp_limit = (unsigned long)sp;
+
+       /* Temporarily switch r1 to sp, call __do_softirq() then restore r1. */
+       asm volatile(
+               "  "PPC_STLU"    1, %2(%1);\n"
+               "  mr              1, %1;\n"
+               "  bl              %3;\n"
+               "  "PPC_LL"      1, 0(1);\n" :
+               "=r"(ret) :
+               "b"(sp), "i"(THREAD_SIZE - STACK_FRAME_OVERHEAD), 
"i"(__do_softirq) :
+               "lr", "xer", "ctr", "memory", "cr0", "cr1", "cr5", "cr6", "cr7",
+               "r0", "r4", "r5", "r6", "r7", "r8", "r9", "r10", "r11", "r12");
+
+       /* Restore stack limit */
+       current->thread.ksp_limit = limit;
+}
+
+static inline void call_do_irq(struct pt_regs *regs, void *sp)
+{
+       register unsigned long r3 asm("r3") = (unsigned long)regs;
+       unsigned long limit = current->thread.ksp_limit;
+
+       /* Adjust the stack limit */
+       current->thread.ksp_limit = (unsigned long)sp;
+
+       /* Temporarily switch r1 to sp, call __do_irq() then restore r1 */
+       asm volatile(
+               "  "PPC_STLU"    1, %2(%1);\n"
+               "  mr              1, %1;\n"
+               "  bl              %3;\n"
+               "  "PPC_LL"      1, 0(1);\n" :
+               "+r"(r3) :
+               "b"(sp), "i"(THREAD_SIZE - STACK_FRAME_OVERHEAD), "i"(__do_irq) 
:
+               "lr", "xer", "ctr", "memory", "cr0", "cr1", "cr5", "cr6", "cr7",
+               "r0", "r4", "r5", "r6", "r7", "r8", "r9", "r10", "r11", "r12");
+
+       /* Restore stack limit */
+       current->thread.ksp_limit = limit;
+}
+#endif
+
  void __do_irq(struct pt_regs *regs)
  {
        unsigned int irq;
diff --git a/arch/powerpc/kernel/misc_32.S b/arch/powerpc/kernel/misc_32.S
index d80212be8698..341a3cd199cb 100644
--- a/arch/powerpc/kernel/misc_32.S
+++ b/arch/powerpc/kernel/misc_32.S
@@ -28,45 +28,6 @@
        .text

/*

- * We store the saved ksp_limit in the unused part
- * of the STACK_FRAME_OVERHEAD
- */
-_GLOBAL(call_do_softirq)
-       mflr    r0
-       stw     r0,4(r1)
-       lwz     r10,THREAD+KSP_LIMIT(r2)
-       stw     r3, THREAD+KSP_LIMIT(r2)
-       stwu    r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r3)
-       mr      r1,r3
-       stw     r10,8(r1)
-       bl      __do_softirq
-       lwz     r10,8(r1)
-       lwz     r1,0(r1)
-       lwz     r0,4(r1)
-       stw     r10,THREAD+KSP_LIMIT(r2)
-       mtlr    r0
-       blr
-
-/*
- * void call_do_irq(struct pt_regs *regs, void *sp);
- */
-_GLOBAL(call_do_irq)
-       mflr    r0
-       stw     r0,4(r1)
-       lwz     r10,THREAD+KSP_LIMIT(r2)
-       stw     r4, THREAD+KSP_LIMIT(r2)
-       stwu    r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r4)
-       mr      r1,r4
-       stw     r10,8(r1)
-       bl      __do_irq
-       lwz     r10,8(r1)
-       lwz     r1,0(r1)
-       lwz     r0,4(r1)
-       stw     r10,THREAD+KSP_LIMIT(r2)
-       mtlr    r0
-       blr
-
-/*
   * This returns the high 64 bits of the product of two 64-bit numbers.
   */
  _GLOBAL(mulhdu)