linux-kernel - Re: Extremely slow IO with a PCMCIA CompactFlash adapter

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Date:	Sun, 2 Aug 2009 11:04:23 -0600
From:	Robert Hancock <hancockrwd@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Jack Byer <ojbyer@....net>, Andreas Mohr <andi@...as.de>,
	linux-kernel@...r.kernel.org
Subject: Re: Extremely slow IO with a PCMCIA CompactFlash adapter

On Sun, Aug 2, 2009 at 4:58 AM, Alan Cox<alan@...rguk.ukuu.org.uk> wrote:
>> irq 3: nobody cared (try booting with the "irqpoll" option)
>> Pid: 23488, comm: modprobe Not tainted 2.6.31-rc4 #2
>> Call Trace:
>
> Something is misrouting interrupts on your machine. COuld be an ACPI bug,
> could be wrong tables in the BIOS etc.
>
>> Now I rebooted with irqpoll and everything looks good in dmesg:
>
> It will recover from the problem sort of
>
>> Now my transfer rate has increased to 20 kilobyte / second read, about
>> 4 times faster than before but still pretty slow.
>
> You should see nearer 200K/sec (PIO 0) but if the device IRQ is being
> lost due to misrouting then the device is being polled off the timer tick
> and that will drastically reduce performance.
>
> So its a firmware/acpi/irq sort of problem not an IDE one. Try running
> with acpi=off and without irqpoll just as a test.

I'm kind of doubtful it's a misrouting, the driver thinks it should be
on IRQ3 and we end up getting spurious interrupts on IRQ3, so I'm
guessing that somehow that card is producing excess interrupts that
we're not expecting, or something?
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