All of lore.kernel.org
 help / color / mirror / Atom feed
From: Paolo Bonzini <pbonzini@redhat.com>
To: "Nicholas A. Bellinger" <nab@linux-iscsi.org>
Cc: Jens Axboe <axboe@kernel.dk>,
	Anthony Liguori <aliguori@us.ibm.com>,
	linux-scsi <linux-scsi@vger.kernel.org>,
	kvm-devel <kvm@vger.kernel.org>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	lf-virt <virtualization@lists.linux-foundation.org>,
	Anthony Liguori <aliguori@linux.vnet.ibm.com>,
	target-devel <target-devel@vger.kernel.org>,
	Zhi Yong Wu <wuzhy@cn.ibm.com>, Christoph Hellwig <hch@lst.de>,
	Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Subject: Re: [PATCH 0/6] tcm_vhost/virtio-scsi WIP code for-3.6
Date: Fri, 06 Jul 2012 07:39:43 +0200	[thread overview]
Message-ID: <4FF67A1F.5080507@redhat.com> (raw)
In-Reply-To: <1341545893.23954.325.camel@haakon2.linux-iscsi.org>

Il 06/07/2012 05:38, Nicholas A. Bellinger ha scritto:
> So I imagine that setting inquiry/vpd/mode via configfs attribs to match
> whatever the guest wants to see (or expects to see) can be enabled
> via /sys/kernel/config/target/core/$HBA/$DEV/[wwn,attrib]/ easily to
> whatever is required.
> 
> However, beyond basic SCSI WWN related bits, I would avoid trying to
> match complex SCSI target state between the in-kernel patch and QEMU
> SCSI.

Agreed.  It should just be the bare minimum to make stable /dev/disk
paths, well, stable between the two backends.

>>> so that it is not possible to migrate one to the other.
>>
>> Migration between different backend types does not seem all that useful.
>> The general rule is you need identical flags on both sides to allow
>> migration, and it is not clear how valuable it is to relax this
>> somewhat.
> 
> I really need to learn more about how QEMU Live migration works wrt to
> storage before saying how this may (or may not) work.

vhost-scsi live migration should be easy to fix.  You need some ioctl or
eventfd mechanism to communicate to userspace that there is no pending
I/O, but you need that anyway also for other operations (as simple as
stopping the VM: QEMU guarantees that the "stop" monitor command returns
only when there is no outstanding I/O).

What worries me most is: 1) the amount of functionality that is lost
with vhost-scsi, especially the new live operations that we're adding to
QEMU; 2) whether any hook we introduce in the QEMU block layer will
cause problems down the road when we set to fix the existing
virtio-blk/virtio-scsi-qemu performance problems.  This is the reason
why I'm reluctant to merge the QEMU bits.  The kernel bits are
self-contained and are much less problematic.

It may well be that _the same_ (or very similar) hooks will be needed by
both tcm_vhost and high-performance userspace virtio backends.  This
would of course remove the objection.

Paolo

  reply	other threads:[~2012-07-06  5:39 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-07-04  4:24 [PATCH 0/6] tcm_vhost/virtio-scsi WIP code for-3.6 Nicholas A. Bellinger
2012-07-04  4:24 ` [PATCH 1/6] vhost: Separate vhost-net features from vhost features Nicholas A. Bellinger
2012-07-04  4:41   ` Asias He
2012-07-04  4:24 ` [PATCH 2/6] vhost: make vhost work queue visible Nicholas A. Bellinger
2012-07-04  4:24 ` Nicholas A. Bellinger
2012-07-04  4:24 ` [PATCH 3/6] vhost: Add vhost_scsi specific defines Nicholas A. Bellinger
2012-07-04  4:24 ` Nicholas A. Bellinger
2012-07-04  4:24 ` [PATCH 4/6] tcm_vhost: Initial merge for vhost level target fabric driver Nicholas A. Bellinger
2012-07-05 17:47   ` Bart Van Assche
2012-07-05 17:47   ` Bart Van Assche
2012-07-05 17:59     ` Bart Van Assche
2012-07-05 17:59     ` Bart Van Assche
2012-07-04  4:24 ` Nicholas A. Bellinger
2012-07-04  4:24 ` [PATCH 5/6] virtio-scsi: Add vdrv->scan for post VIRTIO_CONFIG_S_DRIVER_OK LUN scanning Nicholas A. Bellinger
2012-07-04  4:24 ` Nicholas A. Bellinger
2012-07-04 14:50   ` Paolo Bonzini
2012-07-04  4:24 ` [PATCH 6/6] virtio-scsi: Set shost->max_id=1 for tcm_vhost WWPNs Nicholas A. Bellinger
2012-07-04 14:50   ` Paolo Bonzini
2012-07-05  2:05     ` Nicholas A. Bellinger
2012-07-05  6:42       ` Paolo Bonzini
2012-07-04  4:24 ` Nicholas A. Bellinger
2012-07-04 14:02 ` [PATCH 0/6] tcm_vhost/virtio-scsi WIP code for-3.6 Michael S. Tsirkin
2012-07-04 14:52   ` Paolo Bonzini
2012-07-04 15:05     ` Michael S. Tsirkin
2012-07-04 22:12       ` Anthony Liguori
2012-07-05  1:52         ` Nicholas A. Bellinger
2012-07-05 10:22           ` Paolo Bonzini
2012-07-05 13:53             ` Michael S. Tsirkin
2012-07-05 14:06               ` Anthony Liguori
2012-07-05 14:40                 ` Michael S. Tsirkin
2012-07-05 14:47                   ` Paolo Bonzini
2012-07-05 17:26                     ` Michael S. Tsirkin
2012-07-06  3:01                 ` Nicholas A. Bellinger
2012-07-06  5:43                   ` SCSI Performance regression [was Re: [PATCH 0/6] tcm_vhost/virtio-scsi WIP code for-3.6] James Bottomley
2012-07-06  9:13                     ` Nicholas A. Bellinger
2012-07-06 13:49                       ` James Bottomley
2012-07-06 18:21                         ` Nicholas A. Bellinger
2012-07-06 18:21                         ` Nicholas A. Bellinger
2012-07-06 20:30                     ` [Ksummit-2012-discuss] " Christoph Lameter
2012-07-06 20:30                     ` Christoph Lameter
2012-07-06 22:06                       ` Nicholas A. Bellinger
2012-07-06 22:06                       ` Nicholas A. Bellinger
2012-07-06  3:01                 ` [PATCH 0/6] tcm_vhost/virtio-scsi WIP code for-3.6 Nicholas A. Bellinger
2012-07-05 14:06               ` Anthony Liguori
2012-07-05 14:32               ` Paolo Bonzini
2012-07-05 21:00                 ` Michael S. Tsirkin
2012-07-06  3:38               ` Nicholas A. Bellinger
2012-07-06  5:39                 ` Paolo Bonzini [this message]
2012-07-05 17:53           ` Bart Van Assche
2012-07-05 17:53           ` Bart Van Assche
2012-07-05 19:57             ` Bart Van Assche
2012-07-10  0:29           ` Nicholas A. Bellinger
2012-07-10  0:29           ` Nicholas A. Bellinger
2012-07-05  2:01       ` Nicholas A. Bellinger
2012-07-05  2:01       ` Nicholas A. Bellinger
2012-07-05  9:31         ` Michael S. Tsirkin
2012-07-06  3:13           ` Nicholas A. Bellinger
  -- strict thread matches above, loose matches on Subject: below --
2012-07-04  4:24 Nicholas A. Bellinger

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=4FF67A1F.5080507@redhat.com \
    --to=pbonzini@redhat.com \
    --cc=aliguori@linux.vnet.ibm.com \
    --cc=aliguori@us.ibm.com \
    --cc=axboe@kernel.dk \
    --cc=hch@lst.de \
    --cc=kvm@vger.kernel.org \
    --cc=linux-scsi@vger.kernel.org \
    --cc=mst@redhat.com \
    --cc=nab@linux-iscsi.org \
    --cc=stefanha@linux.vnet.ibm.com \
    --cc=target-devel@vger.kernel.org \
    --cc=virtualization@lists.linux-foundation.org \
    --cc=wuzhy@cn.ibm.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.