Target-devel archive on lore.kernel.org
 help / color / Atom feed
From: Stefan Hajnoczi <stefanha@redhat.com>
To: Mike Christie <michael.christie@oracle.com>
Cc: qemu-devel@nongnu.org, fam@euphon.net,
	linux-scsi@vger.kernel.org, target-devel@vger.kernel.org,
	mst@redhat.com, jasowang@redhat.com, pbonzini@redhat.com,
	virtualization@lists.linux-foundation.org
Subject: Re: [PATCH 00/10] vhost/qemu: thread per IO SCSI vq
Date: Tue, 17 Nov 2020 16:40:43 +0000
Message-ID: <20201117164043.GS131917@stefanha-x1.localdomain> (raw)
In-Reply-To: <1605223150-10888-1-git-send-email-michael.christie@oracle.com>


[-- Attachment #1: Type: text/plain, Size: 2458 bytes --]

On Thu, Nov 12, 2020 at 05:18:59PM -0600, Mike Christie wrote:
> The following kernel patches were made over Michael's vhost branch:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git/log/?h=vhost
> 
> and the vhost-scsi bug fix patchset:
> 
> https://lore.kernel.org/linux-scsi/20201112170008.GB1555653@stefanha-x1.localdomain/T/#t
> 
> And the qemu patch was made over the qemu master branch.
> 
> vhost-scsi currently supports multiple queues with the num_queues
> setting, but we end up with a setup where the guest's scsi/block
> layer can do a queue per vCPU and the layers below vhost can do
> a queue per CPU. vhost-scsi will then do a num_queue virtqueues,
> but all IO gets set on and completed on a single vhost-scsi thread.
> After 2 - 4 vqs this becomes a bottleneck.
> 
> This patchset allows us to create a worker thread per IO vq, so we
> can better utilize multiple CPUs with the multiple queues. It
> implments Jason's suggestion to create the initial worker like
> normal, then create the extra workers for IO vqs with the
> VHOST_SET_VRING_ENABLE ioctl command added in this patchset.

How does userspace find out the tids and set their CPU affinity?

What is the meaning of the new VHOST_SET_VRING_ENABLE ioctl? It doesn't
really "enable" or "disable" the vq, requests are processed regardless.

The purpose of the ioctl isn't clear to me because the kernel could
automatically create 1 thread per vq without a new ioctl. On the other
hand, if userspace is supposed to control worker threads then a
different interface would be more powerful:

  struct vhost_vq_worker_info {
      /*
       * The pid of an existing vhost worker that this vq will be
       * assigned to. When pid is 0 the virtqueue is assigned to the
       * default vhost worker. When pid is -1 a new worker thread is
       * created for this virtqueue. When pid is -2 the virtqueue's
       * worker thread is unchanged.
       *
       * If a vhost worker no longer has any virtqueues assigned to it
       * then it will terminate.
       *
       * The pid of the vhost worker is stored to this field when the
       * ioctl completes successfully. Use pid -2 to query the current
       * vhost worker pid.
       */
      __kernel_pid_t pid;  /* in/out */

      /* The virtqueue index*/
      unsigned int vq_idx; /* in */
  };

  ioctl(vhost_fd, VHOST_SET_VQ_WORKER, &info);

Stefan

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

  parent reply index

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-12 23:18 Mike Christie
2020-11-12 23:19 ` [PATCH 1/1] qemu vhost scsi: add VHOST_SET_VRING_ENABLE support Mike Christie
2020-11-17 11:53   ` Stefan Hajnoczi
2020-12-02  9:59   ` Michael S. Tsirkin
2020-12-02 16:05     ` Michael Christie
2020-11-12 23:19 ` [PATCH 01/10] vhost: remove work arg from vhost_work_flush Mike Christie
2020-11-17 13:04   ` Stefan Hajnoczi
2020-11-12 23:19 ` [PATCH 02/10] vhost scsi: remove extra flushes Mike Christie
2020-11-17 13:07   ` Stefan Hajnoczi
2020-11-12 23:19 ` [PATCH 03/10] vhost poll: fix coding style Mike Christie
2020-11-17 13:07   ` Stefan Hajnoczi
2020-11-12 23:19 ` [PATCH 04/10] vhost: support multiple worker threads Mike Christie
2020-11-12 23:19 ` [PATCH 05/10] vhost: poll support support multiple workers Mike Christie
2020-11-17 15:32   ` Stefan Hajnoczi
2020-11-12 23:19 ` [PATCH 06/10] vhost scsi: make SCSI cmd completion per vq Mike Christie
2020-11-17 16:04   ` Stefan Hajnoczi
2020-11-12 23:19 ` [PATCH 07/10] vhost, vhost-scsi: flush IO vqs then send TMF rsp Mike Christie
2020-11-17 16:05   ` Stefan Hajnoczi
2020-11-12 23:19 ` [PATCH 08/10] vhost: move msg_handler to new ops struct Mike Christie
2020-11-17 16:08   ` Stefan Hajnoczi
2020-11-12 23:19 ` [PATCH 09/10] vhost: add VHOST_SET_VRING_ENABLE support Mike Christie
2020-11-17 16:14   ` Stefan Hajnoczi
2020-11-12 23:19 ` [PATCH 10/10] vhost-scsi: create a woker per IO vq Mike Christie
2020-11-17 16:40 ` Stefan Hajnoczi [this message]
2020-11-17 19:13   ` [PATCH 00/10] vhost/qemu: thread per IO SCSI vq Mike Christie
2020-11-18  9:54     ` Michael S. Tsirkin
2020-11-19 14:00       ` Stefan Hajnoczi
2020-11-18 11:31     ` Stefan Hajnoczi
2020-11-19 14:46       ` Michael S. Tsirkin
2020-11-19 16:11         ` Mike Christie
2020-11-19 16:24           ` Stefan Hajnoczi
2020-11-19 16:43             ` Mike Christie
2020-11-19 17:08               ` Stefan Hajnoczi
2020-11-20  8:45                 ` Stefan Hajnoczi
2020-11-20 12:31                   ` Michael S. Tsirkin
2020-12-01 12:59                     ` Stefan Hajnoczi
2020-12-01 13:45                       ` Stefano Garzarella
2020-12-01 17:43                         ` Stefan Hajnoczi
2020-12-02 10:35                           ` Stefano Garzarella
2020-11-23 15:17                   ` Stefano Garzarella
2020-11-18  5:17   ` Jason Wang
2020-11-18  6:57     ` Mike Christie
2020-11-18  7:19       ` Mike Christie
2020-11-18  7:54       ` Jason Wang
2020-11-18 20:06         ` Mike Christie
2020-11-19  4:35           ` Jason Wang
2020-11-19 15:49             ` Mike Christie

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=20201117164043.GS131917@stefanha-x1.localdomain \
    --to=stefanha@redhat.com \
    --cc=fam@euphon.net \
    --cc=jasowang@redhat.com \
    --cc=linux-scsi@vger.kernel.org \
    --cc=michael.christie@oracle.com \
    --cc=mst@redhat.com \
    --cc=pbonzini@redhat.com \
    --cc=qemu-devel@nongnu.org \
    --cc=target-devel@vger.kernel.org \
    --cc=virtualization@lists.linux-foundation.org \
    /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

Target-devel archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/target-devel/0 target-devel/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 target-devel target-devel/ https://lore.kernel.org/target-devel \
		target-devel@vger.kernel.org
	public-inbox-index target-devel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.target-devel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git