On Thu, 2004-11-04 at 19:27 -0500, Alan Cox wrote:
> 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.
it sounds like HAL should measure how long such a poll takes (shouldn't
be too hard) and then add like 10 times that time to the 2 seconds
interval. On fast hw you get almost a 2 second interval but on really
slow cdroms you still can get decent performance.
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