Messages in this thread | | | Date | Mon, 30 Nov 2009 00:11:51 -0500 | From | Michael Breuer <> | Subject | Re: Problem? intel_iommu=off; perf top shows acpi_os_read_port as extremely busy |
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Ok - one more rather odd (to me) data point... I started playing around with various settings, and traced the calls to acpi_os_read_port.
To summarize: With intel_iommu=off, I see a large percentage of calls to acpi_os_read_port resulting from user apps (portsentry is #1). With intel_iommu=on, NONE of trace points to any user apps - all derive from the idle loop. To make things more interesting, when I enable intel_iommu and disable vt-d in bios, the system performs much better (20% improvement in glxgears, for example), perf top looks like this:
------------------------------------------------------------------------------ PerfTop: 4863 irqs/sec kernel:62.7% [100000 cycles], (all, 8 CPUs) ------------------------------------------------------------------------------
samples pcnt kernel function _______ _____ _______________
2213.00 - 5.5% : acpi_idle_enter_bm 2001.00 - 5.0% : acpi_os_read_port 1544.00 - 3.9% : _spin_lock_irqsave 1075.00 - 2.7% : ioread32 928.00 - 2.3% : find_busiest_group 851.00 - 2.1% : _spin_unlock_irqrestore 823.00 - 2.1% : hpet_next_event 810.00 - 2.0% : tg_shares_up 655.00 - 1.6% : fget_light 641.00 - 1.6% : schedule 639.00 - 1.6% : tick_nohz_stop_sched_tick 638.00 - 1.6% : sub_preempt_count 634.00 - 1.6% : add_preempt_count 548.00 - 1.4% : do_sys_poll 446.00 - 1.1% : trace_hardirqs_off
And additionally, one recurring boot warning I've seen since I first booted this box has disappeared - first boot message of IRQ16 disabled.
I'm thinking that bad VT-D bios is causing trouble even when intel_iommu is disabled.
On 11/29/2009 03:47 PM, Arjan van de Ven wrote: > On Sat, 28 Nov 2009 13:10:21 -0500 > Michael Breuer<mbreuer@majjas.com> wrote: > > >> Ok - my only question then is why things appear so different with >> intel_iommu enabled. >> > something else is even more expensive then :0 > > >
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