Poor disk drive performance with FC3 RC3

[Alan Cox]

On Thu, Nov 04, 2004 at 01:59:48PM -0500, David Zeuthen wrote:
> Basically hal does this (every two seconds)
> 
>  open("/dev/hdc", O_RDONLY|O_NONBLOCK|O_EXCL|O_LARGEFILE) = 0
>  ioctl(0, CDROM_DRIVE_STATUS, 0x7fffffff) = 1
>  close(0) 
> 
> Can some kernel person comment on why this is killing performance on
> the /dev/hda harddrive when the optical drive at /dev/hdb is polled?

Because /dev/hdb is powersaved. Every time you poll it the laptop powers up
the drive (costly on power/time), polls the TOC, replies and a second or so
later powers back down.  During the power up, poll TOC sequence it locks the
bus so your IDE bus spends 1.5 of every 2 seconds jammed by the drive.

We have some bug reports for this from magicdev too.