From: leif.lindholm@arm.com (Leif Lindholm)
To: linux-arm-kernel@lists.infradead.org
Subject: ARM11 MPCore: Adding nop to __delay() doubles the BogoMIPS/lpj
Date: Fri, 29 Jan 2010 12:17:18 -0000 [thread overview]
Message-ID: <000001caa0dd$00b21d90$021658b0$@lindholm@arm.com> (raw)
In-Reply-To: <4B606D92.9020005@googlemail.com>
> -----Original Message-----
> From: linux-arm-kernel-bounces at lists.infradead.org [mailto:linux-arm-
> kernel-bounces at lists.infradead.org] On Behalf Of Dirk Behme
> Sent: 27 January 2010 16:45
> 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():
The reason for this is that the ARM11 MPCore doesn't fold branch
instructions for busy-wait-style loops. Inserting the nop (or any other
non-branch instruction) removes the branch instruction from the
execution stream.
http://infocenter.arm.com/help/topic/com.arm.doc.ddi0360f/ch06s02s04.html
But as Catalin says, this makes no functional difference, even though it
might look "more impressive" :)
/
Leif
next prev parent reply other threads:[~2010-01-29 12:17 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-01-27 16:45 ARM11 MPCore: Adding nop to __delay() doubles the BogoMIPS/lpj Dirk Behme
2010-01-28 13:03 ` Catalin Marinas
2010-01-29 5:08 ` Shilimkar, Santosh
2010-01-29 12:17 ` Leif Lindholm [this message]
-- 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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