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Message-id: <4B11461A.3020408@majjas.com>
Date: Sat, 28 Nov 2009 10:47:38 -0500
From: Michael Breuer <mbreuer@...jas.com>
To: Ingo Molnar <mingo@...e.hu>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>,
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
Ok - did the following in runlevel 3 to avoid the dmar errors I'm
getting with nouveau & vt-d.
In theory, the system was similarly loaded (i.e., doing pretty much
nothing) for both runs.
The sample is consistent with what I've seen previously.
Perhaps there's no issue, or perhaps the issue is with my broken bios
and intel_iommu=on.
Perf top with intel_iommu=off: (snapshop) - acpi_os_read_port is often
#1 and I've seen it over 30%.
------------------------------------------------------------------------------
PerfTop: 3957 irqs/sec kernel:84.0% [100000 cycles], (all, 8 CPUs)
------------------------------------------------------------------------------
samples pcnt kernel function
_______ _____ _______________
3183.00 - 16.7% : _spin_lock
3167.00 - 16.7% : acpi_os_read_port
1053.00 - 5.5% : io_apic_modify_irq
810.00 - 4.3% : hpet_next_event
529.00 - 2.8% : _spin_lock_irqsave
522.00 - 2.7% : io_apic_sync
283.00 - 1.5% : tg_shares_up
270.00 - 1.4% : acpi_idle_enter_bm
259.00 - 1.4% : irq_to_desc
222.00 - 1.2% : i8042_interrupt
213.00 - 1.1% : acpi_hw_validate_io_request
204.00 - 1.1% : ktime_get
180.00 - 0.9% : find_busiest_group
169.00 - 0.9% : _spin_unlock_irqrestore
168.00 - 0.9% : sub_preempt_count
Performance counter stats for 'sleep 1' (10 runs):
8021.581362 task-clock-msecs # 8.009 CPUs ( +-
0.033% )
607 context-switches # 0.000 M/sec ( +-
4.251% )
27 CPU-migrations # 0.000 M/sec ( +-
11.455% )
408 page-faults # 0.000 M/sec ( +-
34.557% )
311405638 cycles # 38.821 M/sec ( +-
6.887% )
85807775 instructions # 0.276 IPC ( +-
13.824% )
2300079 cache-references # 0.287 M/sec ( +-
6.859% )
77314 cache-misses # 0.010 M/sec ( +-
11.184% )
1.001616593 seconds time elapsed ( +- 0.009% )
intel_iommu on:
------------------------------------------------------------------------------
PerfTop: 9941 irqs/sec kernel:81.9% [100000 cycles], (all, 8 CPUs)
------------------------------------------------------------------------------
samples pcnt kernel function
_______ _____ _______________
11465.00 - 20.8% : _spin_lock
3679.00 - 6.7% : io_apic_modify_irq
3295.00 - 6.0% : hpet_next_event
2172.00 - 3.9% : _spin_lock_irqsave
2111.00 - 3.8% : acpi_os_read_port
1094.00 - 2.0% : io_apic_sync
904.00 - 1.6% : find_busiest_group
695.00 - 1.3% : _spin_unlock_irqrestore
686.00 - 1.2% : tg_shares_up
620.00 - 1.1% : acpi_idle_enter_bm
577.00 - 1.0% : add_preempt_count
568.00 - 1.0% : sub_preempt_count
475.00 - 0.9% : audit_filter_syscall
470.00 - 0.9% : schedule
450.00 - 0.8% : tick_nohz_stop_sched_tick
Performance counter stats for 'sleep 1' (10 runs):
8015.967731 task-clock-msecs # 8.003 CPUs ( +-
0.024% )
2628 context-switches # 0.000 M/sec ( +-
20.053% )
124 CPU-migrations # 0.000 M/sec ( +-
20.561% )
3014 page-faults # 0.000 M/sec ( +-
35.573% )
850702031 cycles # 106.126 M/sec ( +-
10.601% )
311032631 instructions # 0.366 IPC ( +-
17.859% )
8578386 cache-references # 1.070 M/sec ( +-
13.894% )
333768 cache-misses # 0.042 M/sec ( +-
21.894% )
1.001656333 seconds time elapsed ( +- 0.008% )
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.)
>
> Thanks,
>
> Ingo
>
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