linux-kernel - Very slow disk speed after "IRQ: nobody cared"

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Date:	Tue, 15 Jun 2010 11:28:18 +0200
From:	Michal Svoboda <michal.svoboda@...nts.felk.cvut.cz>
To:	linux-kernel@...r.kernel.org
Subject: Very slow disk speed after "IRQ: nobody cared"

Hello list,

Sometimes I get a 'nobody cared' message such as this

[  202.078556] irq 16: nobody cared (try booting with the "irqpoll" option)
[  202.078561] Pid: 0, comm: swapper Not tainted 2.6.33 #1
[  202.078563] Call Trace:
[  202.078565]  <IRQ>  [<ffffffff8106ef16>] __report_bad_irq+0x26/0xa0
[  202.078574]  [<ffffffff8106f11a>] note_interrupt+0x18a/0x1d0
[  202.078578]  [<ffffffff8106da0a>] ? handle_IRQ_event+0x4a/0xf0
[  202.078582]  [<ffffffff8106fe3d>] handle_fasteoi_irq+0xcd/0x100
[  202.078587]  [<ffffffff810055dd>] handle_irq+0x1d/0x30
[  202.078590]  [<ffffffff81005257>] do_IRQ+0x67/0xf0
[  202.078595]  [<ffffffff81414493>] ret_from_intr+0x0/0xa
[  202.078597]  <EOI>  [<ffffffff81211b48>] ? acpi_idle_enter_bm+0x224/0x24d
[  202.078606]  [<ffffffff81211b3e>] ? acpi_idle_enter_bm+0x21a/0x24d
[  202.078611]  [<ffffffff8131c72b>] cpuidle_idle_call+0x9b/0x100
[  202.078615]  [<ffffffff8100099c>] cpu_idle+0x9c/0xf0
[  202.078618]  [<ffffffff81003290>] ? kernel_thread_helper+0x0/0x10
[  202.078624]  [<ffffffff813fd9bf>] rest_init+0x8f/0xa0
[  202.078628]  [<ffffffff815ceb31>] start_kernel+0x322/0x32d
[  202.078632]  [<ffffffff815ce2e7>] x86_64_start_reservations+0xf7/0xfb
[  202.078636]  [<ffffffff815ce3d3>] x86_64_start_kernel+0xe8/0xef
[  202.078638] handlers:
[  202.078639] [<ffffffff812af0e0>] (mpt_interrupt+0x0/0x990)
[  202.078645] [<ffffffff812d6ed0>] (usb_hcd_irq+0x0/0x70)
[  202.078649] Disabling IRQ #16

And then my disks go turtle speed:
/dev/sda:
 Timing cached reads:   9180 MB in  2.00 seconds = 4591.89 MB/sec
 Timing buffered disk reads:    8 MB in  3.20 seconds =   2.50 MB/sec

IRQ 16 seems to have something to do with disks:
[   19.703064] scsi6 : ioc0: LSISAS1068E B3, FwRev=00192f00h, Ports=1,
MaxQ=266, IRQ=16
	    CPU0       CPU1       CPU2       CPU3       CPU4       CPU5
	    CPU6       CPU7       
  16:     200124          0          0          0          0          0
               0          0   IO-APIC-fasteoi   ioc0, uhci_hcd:usb3

Is the performance drop caused by the 'disabling IRQ'?  And why would
the 'nobody cared' message be printed in the first place (it happens
only sometimes)? And is there a way out of this (ie. enabling the IRQ)
besides rebooting?

With regards,
Michal Svoboda

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