[ltp] [PATCH] 2.6.17: Unload disks heads before powering down

[Shem Multinymous]

Hi,

I'm adding suspend2-devel to the CC, since this issue probably affects
all suspend2+libata users.

On 9/26/06, Henrique de Moraes Holschuh <hmh@hmh.eng.br> wrote:
> On Tue, 26 Sep 2006, Shem Multinymous wrote:
> > On my box with ata_piix, the kernel is *spinning down* the
> > disks during shutddown.

Ah, found it: drivers/ata/libata-eh.c/ata_eh_suspend() does

	if (dev->class == ATA_DEV_ATA && !(action & ATA_EH_PM_FREEZE)) {
		...
		/* spin down */
		err_mask = ata_do_simple_cmd(dev, ATA_CMD_STANDBYNOW1);


> The EH suspend subroutine does a STANDBY IMMEDIATE command, and that flushes
> caches and spins down the disk, which IS the right thing to do on a system
> shutdown, but quite less so for a system reset.

Any real drawback to doing an UNLOAD IMMEDIATE instead of STANDBY IMMEDIATE?


> Now, teaching the kernel how to differentiate a "regular" scsi bus shutdown,
> from a "will reboot/kexec" scsi bus shutdown is something I have absolutely
> NO CLUE on how to go about doing properly.

Neither do I.


> > Any idea where that comes from, and how it relates to the SuSE head
> > unload patch?


> If you shutdown the scsi bus, the unload patch will spin down the disk.

I'm getting a spindown on reboot (i.e., shutdown) even without the SuSE patch.


> And if you suspend the scsi bus, the regular kernel code will
> spin down the disk as well (at least it should).  And if you
> are going to use the disk to write a image there, what the
> hell are you doing suspending or shutting it down?

My understandin is that Suspend2 suspends all devices, scsi bus
included, in order to get a consistent snapshot; it then resumes the
necessary devices in order to write the snapshot to disk. Currently
this causes a disk spin-down and spin-up, which is bad for the disk
and bad for suspend time.

> I suspect the "so don't do it" finale for this thought is only
> possible with 2.6.18,

What changed here in 2.6.18?
I've tested with vanilla 2.6.18, with 2.6.17.4+suspend2-2.2.7.1 and
with 2.6.17.13+suspend2-2.2.7.6.


> Suspend2 2.2.8 + kernel 2.6.18 is corrupting the page cache here, do *not*
> use it if you value your data.

Does it?! During suspend, you mean? I was just about to test that...

  Shem