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From: Wolfram Sang on 19 Apr 2010 03:30
On Tue, Apr 13, 2010 at 05:27:33PM -0700, Bryan Wu wrote:

> I found the root cause is the polling operation in the mdio_read
> function. When we transfer large files, we experienced many times of
> timeout issue. So I got several question here:

Same here, I saw the 'MDIO Timeout' Message occasionally.

> 1. Need I return -ETIMEDOUT when polling timeout. If I don't return
> -ETIMEOUT, the performance improved a lot. And after check other drivers,
> some don't return anything, some return 0, some return negative value.
> What's the rule for this mdio_read polling timeout case.
>
> 2. How to do polling busy waiting? Normally, we won't buys wait very long
> in polling. But hardware is not perfect every time. Running cpu_relax()
> 10000 times in polling will cause our system response very bad when
> hardware don't set the flag as we expected. Maybe udelay(25) 10 times or
> msleep(1) 10 times is better than that.
>
> I got a patch to recover this issue,
> http://kernel.ubuntu.com/git?p=roc/ubuntu-lucid.git;a=commitdiff;h=5d77e3409b319ca84183bf1d2fd158a9c864e03f.

Can't help with the details, but the patch seems to help here, too
(and not only because of the removed printk ;)).

Regards,

Wolfram

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