Re: Why so much PIO for r/w accesses ?

[Mark Lord <kernel@teksavvy.com>]

On 10-11-21 06:35 PM, Mark Lord wrote:
> While working on something unrelated today,
> I instrumented ata_sff_data_xfer32() to generate a printk() on each invocation.
>
> Imagine then my complete surprise to see that print() being invoked very frequently
> after rebooting with the modified kernel.
>
> ata_sff_data_xfer32() is for PIO read/writes.. something that I don't expect to
> see.
>
> This is an ata_piix system, with a pure SATA SSD.
> Why are we using PIO so much?
> Or am I simply misunderstanding something basic here.. ?
>
> Confused.

Definitely just me being confused.  :)

I changed the printk() into an ata_dev_printk(), and discovered that
all of those reads/writes are targeting the DVD-RW drive, not the SSD.

So this is simply hald or something similar polling for disc-insertion,
and PIO is used (as always) for the PACKET command transfer.

Duh.  :)