Re: [Qemu-devel] virtio-scsi vs. virtio-blk

[Stefan Priebe - Profihost AG <s.priebe@profihost.ag>]

Am 10.08.2012 14:24, schrieb ronnie sahlberg:
> On Fri, Aug 10, 2012 at 10:14 PM, Stefan Priebe - Profihost AG
> <s.priebe@profihost.ag> wrote:
> I dont know the kvm version numbers.
They're the same as qemu.

> But you can check the file
> block/iscsi.c for the version you use  for this :
>
>    .bdrv_aio_discard = iscsi_aio_discard,
# grep 'scsi_aio_discard' block/iscsi.c
  iscsi_aio_discard(BlockDriverState *bs,
      .bdrv_aio_discard = iscsi_aio_discard,

=> so yes

> If it has bdrv_aio_discard then you have support for 'discard' when
> using the scsi emulation. i.e.   -drive ...,if=scsi,...
>
> #ifdef __linux__
>      .bdrv_ioctl       = iscsi_ioctl,
>      .bdrv_aio_ioctl   = iscsi_aio_ioctl,
> #endif

yes too.

> If it has these two lines too, then you have scsi-passthrough and can
> bypass the qemu scsi emulation.
> One way to activate passthough is via scsi-generic:
>      Example:
>          -device lsi -device scsi-generic,drive=MyISCSI \
>          -drive file=iscsi://10.1.1.125/iqn.ronnie.test/1,if=none,id=MyI

When i do this the guest system always uses the sym53c8xx kernel module. 
This results in 70 iops instead of 30000 iops. Is this really correct 
that it uses the very old sym53c8xx kernel module for this device?

used start command:
http://pastebin.com/raw.php?i=23fkaQgc

dmesg from guest:
  dmesg|egrep "sym|scsi"
[    0.000000] Linux version 3.5.0intel (root@neuertestswerverscsi) (gcc 
version 4.4.5 (Debian 4.4.5-8) ) #5 SMP Thu Aug 9 20:27:29 CEST 2012
[    0.291949] scsi0 : ata_piix
[    0.292109] scsi1 : ata_piix
[    0.495217] sym0: <895a> rev 0x0 at pci 0000:00:03.0 irq 10
[    0.498694] sym0: No NVRAM, ID 7, Fast-40, LVD, parity checking
[    0.500565] sym0: SCSI BUS has been reset.
[    0.508603] scsi2 : sym-2.2.3
[    3.512544] sym0: unknown interrupt(s) ignored, ISTAT=0x5 DSTAT=0x80 
SIST=0x0
[    3.514004] scsi 2:0:0:0: Direct-Access     NEXENTA  NEXENTASTOR 
  1.0  PQ: 0 ANSI: 5
[    3.514414] scsi target2:0:0: tagged command queuing enabled, command 
queue depth 16.
[    3.514820] scsi target2:0:0: Beginning Domain Validation
[    3.518370] scsi target2:0:0: Domain Validation skipping write tests
[    3.518772] scsi target2:0:0: Ending Domain Validation


Thanks a lot!

Stefan