linux-kernel - Re: Problem? intel_iommu=off; perf top shows acpi_os_read

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Message-ID: <1259422066.2155.4.camel@laptop>
Date:	Sat, 28 Nov 2009 16:27:46 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Michael Breuer <mbreuer@...jas.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Len Brown <lenb@...nel.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Problem? intel_iommu=off; perf top shows acpi_os_read_port as
 extremely busy

On Sat, 2009-11-28 at 08:18 +0100, Ingo Molnar wrote:
> * Michael Breuer <mbreuer@...jas.com> wrote:
> 
> > Having given up for now on VT-D, I rebooted 2.6.38 rc8 with 
> > intel_iommu=off. Whilst my myriad of broken bios issues cleared, I now 
> > see in perf top acpi_os_read_port as continually the busiest function. 
> > With intel_iommu enabled, _spin_lock was always on top, and nothing 
> > else was notable.
> > 
> > This seems odd to me, perhaps this will make sense to someone else.
> > 
> > FWIW, I'm running on an Asus p6t deluxe v2; ht enabled; no errors or 
> > oddities in dmesg or /var/log/messages.
> 
> Could you post the perf top output please?
> 
> Also, could you also post the output of:
> 
> 	perf stat -a --repeat 10 sleep 1
> 
> this will show us how idle the system is. (My guess is that your system 
> is idle and perf top shows acpi_os_read_port because the system goes to 
> idle via ACPI methods and PIO is slow. In that case all is nominal and 
> your system is fine. But it's hard to tell without more details.)

Isn't there also a list of symbols it won't display? Can't find either
the list nor the switch to turn it off (really didn't look hard), but
acme might know.



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