From: Keith Owens <kaos@sgi.com>
To: linux-ia64@vger.kernel.org
Subject: [Linux-ia64] Re: strange performance behaviour with floats
Date: Mon, 24 Feb 2003 01:45:10 +0000 [thread overview]
Message-ID: <marc-linux-ia64-105590709805910@msgid-missing> (raw)
On Fri, 21 Feb 2003 18:30:32 -0800,
David Mosberger <davidm@napali.hpl.hp.com> wrote:
>1-cycle loops are
>never optimal on McKinley (that's why the Linux bogomips comes out at
>1438 instead of 2000, for example), though I don't know the exact
>micro-architectural details that cause this.
--- include/asm-ia64/delay.h
+++ include/asm-ia64/delay.h
@@ -71,7 +71,7 @@
__asm__ __volatile__("mov %0=ar.lc;;" : "=r"(saved_ar_lc));
__asm__ __volatile__("mov ar.lc=%0;;" :: "r"(loops - 1));
- __asm__ __volatile__("1:\tbr.cloop.sptk.few 1b;;");
+ __asm__ __volatile__("1:\tnop 0;nop 0;nop 0;br.cloop.sptk.few 1b;;");
__asm__ __volatile__("mov ar.lc=%0" :: "r"(saved_ar_lc));
}
generated a two bundle loop as you suggested, but BogoMIPS went down,
not up.
Original code, one bundle br.cloop:
CPU 0: base freq 0.000MHz, ITC ratio=9/2, ITC freqê0.000MHz
Calibrating delay loop... 1347.52 BogoMIPS
Modified code, two bundle br.cloop:
CPU 0: base freq 0.000MHz, ITC ratio=9/2, ITC freqê0.000MHz
Calibrating delay loop... 898.68 BogoMIPS
processor : 0
vendor : GenuineIntel
arch : IA-64
family : Itanium 2
model : 0
revision : 6
archrev : 0
features : branchlong
cpu number : 0
cpu regs : 4
cpu MHz : 900.000000
itc MHz : 900.000000
next reply other threads:[~2003-02-24 1:45 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-02-24 1:45 Keith Owens [this message]
2003-02-24 1:50 ` [Linux-ia64] Re: strange performance behaviour with floats David Mosberger
2003-02-24 2:01 ` Keith Owens
2003-02-24 2:16 ` David Mosberger
2003-02-24 2:25 ` Keith Owens
2003-02-24 19:12 ` David Mosberger
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