RE: [Linux-ia64] Single bundle loops on Itanium-2 sometimes run slow

From: Mallick, Asit K <asit.k.mallick_at_intel.com>
Date: 2003-03-15 07:26:49
Jack,

We are looking at this. I am assuming that if the bundle is aligned then
you do not see this problem. Is my assumption correct?
Thanks,
Asit


> -----Original Message-----
> From: David Mosberger [mailto:davidm@napali.hpl.hp.com]
> Sent: Friday, March 14, 2003 11:47 AM
> To: Jack Steiner
> Cc: linux-ia64@linuxia64.org
> Subject: Re: [Linux-ia64] Single bundle loops on Itanium-2 sometimes
run
> slow
> 
> >>>>> On Fri, 14 Mar 2003 12:51:43 -0600 (CST), Jack Steiner
> <steiner@sgi.com> said:
> 
>   Jack> SUMMARY: It appears that if a single bundle misaligned loop is
>   Jack> interrupted (timer, etc), when the loop is resumed, it
>   Jack> sometimes runs at about 1/3 the normal rate until the loop
>   Jack> completes. (I dont mean 1 or a few iterations of the loop!!)
> 
>   Jack> 	4000000000000eb0: [MIB] adds r8=1,r32
>   Jack> 4000000000000eb6: adds r32=-1,r32 4000000000000ebc:
>   Jack> br.cloop.sptk.few 4000000000000eb0 <compute+0x60>;;
> 
> 
>   Jack> If "noise" is present, pfmon shows significant lost cycles due
>   Jack> to BE_LOST_BW_DUE_TO_FE_BR_ILOCK.  A 15 second sample shows:
>   Jack> BE_LOST_BW_DUE_TO_FE_BR_ILOCK = 423 for good run
>   Jack> BE_LOST_BW_DUE_TO_FE_BR_ILOCK = 105935651 for noisy run
> 
>   Jack> Changing the test so that code is at different addresses
>   Jack> effects the likelyhood that noise will occur. Sometimes noise
>   Jack> occurs on only a subset of the cpus. Sometimes booting a
>   Jack> different kernel changes the likelyhood of seeing noise.
> 
>   Jack> Has anyone seen this behavior or have an explanation.
> 
> Can you check whether the problem goes away when you turn the loop
> into a 2-cycle loop?  My bet is that it will.
> 
> 	--david
> 
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Received on Fri Mar 14 12:26:55 2003

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