From: dirk.behme@googlemail.com (Dirk Behme)
To: linux-arm-kernel@lists.infradead.org
Subject: ARM11 MPCore: Adding nop to __delay() doubles the BogoMIPS/lpj
Date: Wed, 27 Jan 2010 17:45:06 +0100 [thread overview]
Message-ID: <4B606D92.9020005@googlemail.com> (raw)
On a 400MHz ARM11 MPCore system (NEC NaviEngine based) with kernel
2.6.32 we found that BogoMIPS/loops per jiffies ~doubles (see below
[1]) by adding a nop to __delay():
--- a/arch/arm/lib/delay.S
+++ b/arch/arm/lib/delay.S
@@ -41,6 +41,9 @@ ENTRY(__const_udelay) @ 0 <= r0 <= 0x
@ Delay routine
ENTRY(__delay)
+#if defined(CONFIG_CPU_V6) && defined(CONFIG_SMP)
+ nop
+#endif
subs r0, r0, #1
#if 0
movls pc, lr
Any ideas what might happen here?
Many thanks and best regards
Dirk
[1] 2.6.32 without and with additional nop in __delay():
====> Clean 2.6.32 without nop in __delay():
...
Calibrating delay loop... 159.74 BogoMIPS (lpj=798720)
Mount-cache hash table entries: 512
CPU: Testing write buffer coherency: ok
Calibrating local timer... 199.98MHz.
CPU1: Booted secondary processor
Calibrating delay loop... 159.33 BogoMIPS (lpj=796672)
CPU2: Booted secondary processor
Calibrating delay loop... 159.74 BogoMIPS (lpj=798720)
Brought up 3 CPUs
SMP: Total of 3 processors activated (478.82 BogoMIPS).
...
Disassembly:
|@ Delay routine
|ENTRY(__delay)
C0940600|E2500001 __delay: subs r0,r0,#0x1
C0940604|8AFFFFFD bhi 0xC0940600 ; __delay
C0940608|E1A0F00E cpy pc,r14
====> With an additional nop in __delay():
...
Calibrating delay loop... 398.95 BogoMIPS (lpj=1994752)
Mount-cache hash table entries: 512
CPU: Testing write buffer coherency: ok
Calibrating local timer... 199.97MHz.
CPU1: Booted secondary processor
Calibrating delay loop... 398.95 BogoMIPS (lpj=1994752)
CPU2: Booted secondary processor
Calibrating delay loop... 398.95 BogoMIPS (lpj=1994752)
Brought up 3 CPUs
SMP: Total of 3 processors activated (1196.85 BogoMIPS).
...
Disassembly:
|@ Delay routine
|ENTRY(__delay)
|#if defined(CONFIG_CPU_V6) && defined(CONFIG_SMP)
C0940600|E320F000 __delay: nop
|#endif
C0940604|E2500001 subs r0,r0,#0x1
C0940608|8AFFFFFC bhi 0xC0940600 ; __delay
C094060C|E1A0F00E cpy pc,r14
next reply other threads:[~2010-01-27 16:45 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-01-27 16:45 Dirk Behme [this message]
2010-01-28 13:03 ` ARM11 MPCore: Adding nop to __delay() doubles the BogoMIPS/lpj Catalin Marinas
2010-01-29 5:08 ` Shilimkar, Santosh
2010-01-29 12:17 ` Leif Lindholm
-- strict thread matches above, loose matches on Subject: below --
2010-01-29 14:54 Uwe Kleine-König
2010-01-29 15:17 ` Leif Lindholm
2010-01-29 15:26 ` Russell King - ARM Linux
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