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From: ronnie sahlberg <ronniesahlberg@gmail.com>
To: Stefan Priebe - Profihost AG <s.priebe@profihost.ag>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	qemu-devel <qemu-devel@nongnu.org>,
	Stefan Hajnoczi <stefanha@gmail.com>
Subject: Re: [Qemu-devel] virtio-scsi vs. virtio-blk
Date: Fri, 10 Aug 2012 22:24:56 +1000	[thread overview]
Message-ID: <CAN05THT_uwYg5-fCEAqip7MerSbDXyGjj6PO73frxfOfrEPaBw@mail.gmail.com> (raw)
In-Reply-To: <5024FB17.7060706@profihost.ag>

On Fri, Aug 10, 2012 at 10:14 PM, Stefan Priebe - Profihost AG
<s.priebe@profihost.ag> wrote:
> Am 10.08.2012 14:04, schrieb ronnie sahlberg:
>
>> On Fri, Aug 10, 2012 at 9:57 PM, Stefan Priebe - Profihost AG
>> <s.priebe@profihost.ag> wrote:
>>>
>>> Am 10.08.2012 13:12, schrieb ronnie sahlberg:
>>>
>>>> You want discard to work?
>>>
>>>
>>> Yes
>>>
>>>
>>>> You are using qemu 1.0 ?
>>>
>>>
>>> actual qemu-kvm git
>>>
>>>
>>>> So you dont have the qemu support for scsi-generic passthrough to iscsi
>>>> devices.
>>>
>>>
>>> Why?
>>>
>>
>> scsi-generic passthrough I think was added for iscsi in 1.1
>> so in 1.0 your guest will talk scsi to qemu, and invoke the
>> scsi-emulation in qemu.
>> It then will call functions like 'bdrv_aio_discard()" in libiscsi
>> that will translate it back into a scsi command again and pass it to
>> the target.
>>
>> It still works, it just means you have a small degradation of
>> performance compared to if you could send the SCSI CDB straight
>> through to the iscsi target as you can in qemu 1.1
>> Very likely so small performance hit that you can not even measure it.
>
>
> which version are you talking about? I use qemu-kvm.git so this is upcomming
> 1.2 and i use libiscsi 1.5.0.

I dont know the kvm version numbers.

But you can check the file
block/iscsi.c for the version you use  for this :

  .bdrv_aio_discard = iscsi_aio_discard,

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

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


regards
ronnie sahlberg

  reply	other threads:[~2012-08-10 12:25 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-08-08 15:21 [Qemu-devel] virtio-scsi vs. virtio-blk Stefan Priebe
2012-08-08 16:17 ` Paolo Bonzini
2012-08-08 17:12   ` Stefan Priebe
2012-08-08 17:37     ` Paolo Bonzini
2012-08-09  6:13   ` Stefan Priebe
2012-08-09  7:01     ` Paolo Bonzini
2012-08-09  7:07       ` Stefan Priebe
2012-08-09  7:19         ` Paolo Bonzini
2012-08-09  7:41           ` Stefan Priebe
2012-08-09  7:53             ` Paolo Bonzini
2012-08-09  8:00               ` Stefan Priebe
2012-08-09  8:03                 ` Paolo Bonzini
2012-08-09  9:18             ` Stefan Hajnoczi
2012-08-09 10:17               ` Stefan Priebe - Profihost AG
2012-08-09 11:04                 ` Stefan Hajnoczi
2012-08-09 11:10                   ` Paolo Bonzini
2012-08-09 11:24                   ` Stefan Priebe - Profihost AG
2012-08-09 12:08                   ` Stefan Priebe - Profihost AG
2012-08-09 12:19                     ` Paolo Bonzini
2012-08-09 12:31                       ` Stefan Priebe - Profihost AG
2012-08-09 12:44                         ` Paolo Bonzini
2012-08-09 15:41                           ` Stefan Priebe - Profihost AG
2012-08-09 12:52                         ` ronnie sahlberg
2012-08-09 13:15                           ` Paolo Bonzini
2012-08-09 13:39                             ` Stefan Priebe - Profihost AG
2012-08-09 13:42                               ` Paolo Bonzini
2012-08-09 13:52                                 ` Stefan Priebe - Profihost AG
2012-08-09 14:35                                   ` Paolo Bonzini
2012-08-09 14:25                                 ` Stefan Priebe - Profihost AG
2012-08-10  9:22                 ` Stefan Priebe - Profihost AG
2012-08-10 10:20                   ` Paolo Bonzini
2012-08-10 10:28                     ` Stefan Priebe - Profihost AG
2012-08-10 10:30                       ` Paolo Bonzini
2012-08-10 11:12                         ` ronnie sahlberg
2012-08-10 11:57                           ` Stefan Priebe - Profihost AG
2012-08-10 12:04                             ` ronnie sahlberg
2012-08-10 12:14                               ` Stefan Priebe - Profihost AG
2012-08-10 12:24                                 ` ronnie sahlberg [this message]
2012-08-10 12:35                                   ` Stefan Priebe - Profihost AG
2012-08-10 12:39                                     ` Paolo Bonzini
2012-08-10 12:43                                       ` Stefan Priebe - Profihost AG
2012-08-10 11:20                         ` ronnie sahlberg
2012-08-10 11:54                           ` Stefan Priebe - Profihost AG
2012-08-10 11:58                             ` ronnie sahlberg
2012-08-10 12:38                               ` Stefan Priebe - Profihost AG
2012-08-10 11:49                         ` Stefan Priebe - Profihost AG

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