linux-kernel - [PATCH 54/72] Blackfin: optimize fixed code handling for the most common case

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Date:	Mon, 14 Sep 2009 16:07:58 -0400
From:	Mike Frysinger <vapier@...too.org>
To:	linux-kernel@...r.kernel.org
Cc:	uclinux-dist-devel@...ckfin.uclinux.org
Subject: [PATCH 54/72] Blackfin: optimize fixed code handling for the most common case

The majority of the time we are returning to user space, it is not in the
fixed atomic code region.  So rather than branch to a function where we
check the PC and return, do the check inline and branch only when needed.

Also, tweak some of the fixed code handling based on assumptions we are
aware of but cannot be expressed in C.

Signed-off-by: Mike Frysinger <vapier@...too.org>
---
 arch/blackfin/kernel/process.c    |   10 ++--------
 arch/blackfin/mach-common/entry.S |    6 ++++++
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/blackfin/kernel/process.c b/arch/blackfin/kernel/process.c
index 9da36ba..f5b2861 100644
--- a/arch/blackfin/kernel/process.c
+++ b/arch/blackfin/kernel/process.c
@@ -282,25 +282,19 @@ void finish_atomic_sections (struct pt_regs *regs)
 {
 	int __user *up0 = (int __user *)regs->p0;
 
-	if (regs->pc < ATOMIC_SEQS_START || regs->pc >= ATOMIC_SEQS_END)
-		return;
-
 	switch (regs->pc) {
 	case ATOMIC_XCHG32 + 2:
 		put_user(regs->r1, up0);
-		regs->pc += 2;
+		regs->pc = ATOMIC_XCHG32 + 4;
 		break;
 
 	case ATOMIC_CAS32 + 2:
 	case ATOMIC_CAS32 + 4:
 		if (regs->r0 == regs->r1)
+	case ATOMIC_CAS32 + 6:
 			put_user(regs->r2, up0);
 		regs->pc = ATOMIC_CAS32 + 8;
 		break;
-	case ATOMIC_CAS32 + 6:
-		put_user(regs->r2, up0);
-		regs->pc += 2;
-		break;
 
 	case ATOMIC_ADD32 + 2:
 		regs->r0 = regs->r1 + regs->r0;
diff --git a/arch/blackfin/mach-common/entry.S b/arch/blackfin/mach-common/entry.S
index e7eb163..a9b15aa 100644
--- a/arch/blackfin/mach-common/entry.S
+++ b/arch/blackfin/mach-common/entry.S
@@ -1025,6 +1025,12 @@ ENTRY(_schedule_and_signal_from_int)
 #endif
 	sti r0;
 
+	/* finish the userspace "atomic" functions for it */
+	r1 = FIXED_CODE_END;
+	r2 = [sp + PT_PC];
+	cc = r1 <= r2;
+	if cc jump .Lresume_userspace (bp);
+
 	r0 = sp;
 	sp += -12;
 	call _finish_atomic_sections;
-- 
1.6.4.2

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