Re: DMA doesn't work since "make ata port as parent device of scsi host"

[Lin Ming <ming.m.lin@intel.com>]

On Thu, 2012-03-15 at 08:48 +0100, Jörg Sommer wrote:
> Lin Ming hat am Thu 15. Mar, 11:26 (+0800) geschrieben:
> > On Thu, 2012-03-15 at 09:59 +0800, Lin Ming wrote:
> > > On Thu, 2012-03-15 at 02:48 +0100, Jörg Sommer wrote:
> > > > Hi,
> > > > 
> > > > I'm getting these messages in a KVM virtualized host and the access to
> > > > the disks is very slow. Using libata.dma=0 suppresses the warnings, but
> > > > the disks are still slow.
> > > 
> > > Hi Jörg,
> > > 
> > > Let me try to reproduce this issue first.
> > 
> > I tried below commands on x86_32, but can't reproduce it.
> > 
> > qemu-system-i386 -kernel /root/vmlinuz-3.3.0-rc7 -append "root=/dev/sda1
> > zcache" -hda /root/debian-32.img -hdb /root/data.img
> > 
> > Maybe because i386 uses different ata controller than ppc(ata_piix vs
> > pata-macio).
> > 
> > I'll try qemu-system-ppc.
> > 
> > Did you need to run some workload to trigger these warings?
> > Or did you get these warnings right after booting the VM?
> 
> These warnings come up before »INIT started«. I don't have to do
> anything, just wait and see.
> 
> # truncate -s100M /mnt/data/new
> # mke2fs -Fq /mnt/data/new
> # mount -o loop /mnt/data/new /mnt/other
> # cp --parents /bin/zsh-static /mnt/other/zsh
> # umount /mnt/other
> # qemu-system-ppc -enable-kvm -M mac99 -cpu G4 -k de -kernel /boot/vmlinuz-3.3.0-rc5-04520-g8d233c0 -append 'root=/dev/sda ro console=ttyPZ0 init=/zsh' -hda /mnt/data/new
> 
> I've uploaded my config and the kernel:
> http://alioth.debian.org/~jo-guest/config-3.3.0-rc5-04520-g8d233c0
> http://alioth.debian.org/~jo-guest/vmlinuz-3.3.0-rc5-04520-g8d233c0
> 
> You have to switch to the serial console (Ctrl-Alt-3 or with -nographic
> Ctrl-a c). All kernel messages arrive there.
> 
> > Would you please try to disable ata port runtime pm?
> > You can disable it by, for example,
> 
> Is this also possible with a kernel parameter? It takes very long until I
> get a shell prompt.

No, but you can try below debug patch to disable port runtime pm.

diff --git a/drivers/ata/libata-transport.c b/drivers/ata/libata-transport.c
index 74aaee3..8def3fc 100644
--- a/drivers/ata/libata-transport.c
+++ b/drivers/ata/libata-transport.c
@@ -293,7 +293,6 @@ int ata_tport_add(struct device *parent,
 
 	device_enable_async_suspend(dev);
 	pm_runtime_set_active(dev);
-	pm_runtime_enable(dev);
 
 	transport_add_device(dev);
 	transport_configure_device(dev);


> 
> Bye, Jörg.