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[v3,01/11] alpha: Add clear_bit_unlock_is_negative_byte implementation

Message ID 20200416220130.13343-2-willy@infradead.org (mailing list archive)
State New, archived
Headers show
Series Make PageWriteback use the PageLocked optimisation | expand

Commit Message

Matthew Wilcox April 16, 2020, 10:01 p.m. UTC 
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Copy and paste the clear_bit_unlock() implementation, and test the temp
variable to see if it has bit 7 set.  Saves two instructions: a load
and a compare:

      860:      01 31 20 44     andnot  t0,0x1,t0
      864:      00 00 30 b8     stl_c   t0,0(a0)
      868:      67 1b 20 e4     beq     t0,7608 <generic_file_write_iter+0x218>
-     86c:      00 00 30 a0     ldl     t0,0(a0)
-     870:      01 10 30 44     and     t0,0x80,t0
-     874:      a1 03 e1 43     cmpult  zero,t0,t0
-     878:      01 00 20 f4     bne     t0,880 <unlock_page+0x40>
-     87c:      01 80 fa 6b     ret
+     86c:      01 10 30 44     and     t0,0x80,t0
+     870:      03 00 20 f4     bne     t0,880 <unlock_page+0x40>
+     874:      01 80 fa 6b     ret

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: linux-alpha@vger.kernel.org
---
 arch/alpha/include/asm/bitops.h | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)
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Patch

diff --git a/arch/alpha/include/asm/bitops.h b/arch/alpha/include/asm/bitops.h
index 5adca78830b5..f9af2401bd23 100644
--- a/arch/alpha/include/asm/bitops.h
+++ b/arch/alpha/include/asm/bitops.h
@@ -79,6 +79,29 @@  clear_bit_unlock(unsigned long nr, volatile void * addr)
 	clear_bit(nr, addr);
 }
 
+static inline bool clear_bit_unlock_is_negative_byte(unsigned int nr,
+						     volatile unsigned long *p)
+{
+	unsigned long temp;
+	int *m = ((int *)p) + (nr >> 5);
+
+	smp_mb();
+	__asm__ __volatile__(
+	"1:	ldl_l %0,%3\n"
+	"	bic %0,%2,%0\n"
+	"	stl_c %0,%1\n"
+	"	beq %0,2f\n"
+	".subsection 2\n"
+	"2:	br 1b\n"
+	".previous"
+	:"=&r" (temp), "=m" (*m)
+	:"Ir" (1UL << (nr & 31)), "m" (*m));
+
+	return temp & 128;
+}
+#define clear_bit_unlock_is_negative_byte \
+	clear_bit_unlock_is_negative_byte
+
 /*
  * WARNING: non atomic version.
  */