linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Jason Wang <jasowang@redhat.com>
To: "Liu, Jing2" <jing2.liu@linux.intel.com>,
	Zha Bin <zhabin@linux.alibaba.com>,
	linux-kernel@vger.kernel.org
Cc: virtio-dev@lists.oasis-open.org, slp@redhat.com, mst@redhat.com,
	qemu-devel@nongnu.org, chao.p.peng@linux.intel.com,
	gerry@linux.alibaba.com
Subject: Re: [virtio-dev] Re: [PATCH v2 4/5] virtio-mmio: add MSI interrupt feature support
Date: Tue, 11 Feb 2020 12:02:50 +0800	[thread overview]
Message-ID: <ad96269f-753d-54b8-a4ae-59d1595dd3b2@redhat.com> (raw)
In-Reply-To: <c42c8b49-5357-f341-2942-ba84afc25437@linux.intel.com>


On 2020/2/11 上午11:35, Liu, Jing2 wrote:
>
> On 2/11/2020 11:17 AM, Jason Wang wrote:
>>
>> On 2020/2/10 下午5:05, Zha Bin wrote:
>>> From: Liu Jiang<gerry@linux.alibaba.com>
>>>
>>> Userspace VMMs (e.g. Qemu microvm, Firecracker) take advantage of using
>>> virtio over mmio devices as a lightweight machine model for modern
>>> cloud. The standard virtio over MMIO transport layer only supports one
>>> legacy interrupt, which is much heavier than virtio over PCI transport
>>> layer using MSI. Legacy interrupt has long work path and causes 
>>> specific
>>> VMExits in following cases, which would considerably slow down the
>>> performance:
>>>
>>> 1) read interrupt status register
>>> 2) update interrupt status register
>>> 3) write IOAPIC EOI register
>>>
>>> We proposed to add MSI support for virtio over MMIO via new feature
>>> bit VIRTIO_F_MMIO_MSI[1] which increases the interrupt performance.
>>>
>>> With the VIRTIO_F_MMIO_MSI feature bit supported, the virtio-mmio MSI
>>> uses msi_sharing[1] to indicate the event and vector mapping.
>>> Bit 1 is 0: device uses non-sharing and fixed vector per event mapping.
>>> Bit 1 is 1: device uses sharing mode and dynamic mapping.
>>
>>
>> I believe dynamic mapping should cover the case of fixed vector?
>>
> Actually this bit *aims* for msi sharing or msi non-sharing.
>
> It means, when msi sharing bit is 1, device doesn't want vector per queue
>
> (it wants msi vector sharing as name) and doesn't want a high 
> interrupt rate.
>
> So driver turns to !per_vq_vectors and has to do dynamical mapping.
>
> So they are opposite not superset.
>
> Thanks!
>
> Jing


I think you need add more comments on the command.

E.g if I want to map vector 0 to queue 1, how do I need to do?

write(1, queue_sel);
write(0, vector_sel);

?

Thanks


>
>
>> Thanks
>>
>>
>>
>> ---------------------------------------------------------------------
>> To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org
>> For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org
>>
>


  reply	other threads:[~2020-02-11  4:03 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-10  9:05 [PATCH v2 0/5] virtio mmio specification enhancement Zha Bin
2020-02-10  9:05 ` [PATCH v2 1/5] virtio-mmio: add notify feature for per-queue Zha Bin
2020-02-11 10:50   ` Michael S. Tsirkin
2020-02-11 11:33   ` Michael S. Tsirkin
2020-02-12  3:39     ` Jason Wang
2020-02-12  8:18       ` Michael S. Tsirkin
2020-02-12  8:53         ` Jason Wang
2020-02-12  9:33           ` Jason Wang
2020-02-12  9:55             ` Michael S. Tsirkin
2020-02-13  3:38               ` Jason Wang
2020-02-10  9:05 ` [PATCH v2 2/5] virtio-mmio: refactor common functionality Zha Bin
2020-02-11 11:19   ` Michael S. Tsirkin
2020-02-12  2:58     ` [virtio-dev] " Liu, Jing2
2020-02-12  7:29       ` Michael S. Tsirkin
2020-02-10  9:05 ` [PATCH v2 3/5] virtio-mmio: create a generic MSI irq domain Zha Bin
2020-02-11 11:16   ` Michael S. Tsirkin
2020-02-12  7:40   ` Michael S. Tsirkin
2020-02-10  9:05 ` [PATCH v2 4/5] virtio-mmio: add MSI interrupt feature support Zha Bin
2020-02-11  3:17   ` Jason Wang
2020-02-11  3:35     ` [virtio-dev] " Liu, Jing2
2020-02-11  4:02       ` Jason Wang [this message]
     [not found]         ` <5522f205-207b-b012-6631-3cc77dde3bfe@linux.intel.com>
2020-02-11  7:40           ` Jason Wang
2020-02-11 11:58             ` Michael S. Tsirkin
2020-02-11 12:04               ` Jason Wang
2020-02-11 12:08                 ` Michael S. Tsirkin
2020-02-11 12:18                   ` Jason Wang
2020-02-11 14:00                     ` Michael S. Tsirkin
2020-02-12  9:03                       ` Jason Wang
2020-02-12  9:15                         ` Michael S. Tsirkin
     [not found]             ` <4c19292f-9d25-a859-3dde-6dd5a03fdf0b@linux.intel.com>
2020-02-12  7:33               ` Michael S. Tsirkin
2020-02-12  9:06               ` Jason Wang
2020-02-12  9:16                 ` Michael S. Tsirkin
2020-02-13  3:40                   ` Jason Wang
2020-02-11 11:21       ` Michael S. Tsirkin
2020-02-11 11:11   ` Michael S. Tsirkin
2020-02-10  9:05 ` [PATCH v2 5/5] x86: virtio-mmio: support virtio-mmio with MSI for x86 Zha Bin
2020-02-11 11:14   ` Michael S. Tsirkin
2020-02-10 11:44 ` [PATCH v2 0/5] virtio mmio specification enhancement Michael S. Tsirkin
2020-02-11 16:05   ` Chao Peng
2020-02-11 10:57     ` Michael S. Tsirkin

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=ad96269f-753d-54b8-a4ae-59d1595dd3b2@redhat.com \
    --to=jasowang@redhat.com \
    --cc=chao.p.peng@linux.intel.com \
    --cc=gerry@linux.alibaba.com \
    --cc=jing2.liu@linux.intel.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mst@redhat.com \
    --cc=qemu-devel@nongnu.org \
    --cc=slp@redhat.com \
    --cc=virtio-dev@lists.oasis-open.org \
    --cc=zhabin@linux.alibaba.com \
    --subject='Re: [virtio-dev] Re: [PATCH v2 4/5] virtio-mmio: add MSI interrupt feature support' \
    /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

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).