From: Stefan Hajnoczi <stefanha@gmail.com>
To: Mike Christie <michael.christie@oracle.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>, fam <fam@euphon.net>,
linux-scsi <linux-scsi@vger.kernel.org>,
Jason Wang <jasowang@redhat.com>,
qemu-devel <qemu-devel@nongnu.org>,
Linux Virtualization <virtualization@lists.linux-foundation.org>,
target-devel <target-devel@vger.kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Stefano Garzarella <sgarzare@redhat.com>
Subject: Re: [PATCH 00/10] vhost/qemu: thread per IO SCSI vq
Date: Fri, 20 Nov 2020 08:45:49 +0000 [thread overview]
Message-ID: <CAJSP0QVu4P6c+kdFkhw1S_OEaj7B-eiDqFOVDxWAaSOcsAADrA@mail.gmail.com> (raw)
In-Reply-To: <CAJSP0QUfqd=QNFa-RikH4dVcLmfcP-pYCwznP3W0zobYkM+KDw@mail.gmail.com>
On Thu, Nov 19, 2020 at 5:08 PM Stefan Hajnoczi <stefanha@gmail.com> wrote:
>
> On Thu, Nov 19, 2020 at 4:43 PM Mike Christie
> <michael.christie@oracle.com> wrote:
> >
> > On 11/19/20 10:24 AM, Stefan Hajnoczi wrote:
> > > On Thu, Nov 19, 2020 at 4:13 PM Mike Christie
> > > <michael.christie@oracle.com> wrote:
> > >>
> > >> On 11/19/20 8:46 AM, Michael S. Tsirkin wrote:
> > >>> On Wed, Nov 18, 2020 at 11:31:17AM +0000, Stefan Hajnoczi wrote:
> > > struct vhost_run_worker_info {
> > > struct timespec *timeout;
> > > sigset_t *sigmask;
> > >
> > > /* List of virtqueues to process */
> > > unsigned nvqs;
> > > unsigned vqs[];
> > > };
> > >
> > > /* This blocks until the timeout is reached, a signal is received, or
> > > the vhost device is destroyed */
> > > int ret = ioctl(vhost_fd, VHOST_RUN_WORKER, &info);
> > >
> > > As you can see, userspace isn't involved with dealing with the
> > > requests. It just acts as a thread donor to the vhost driver.
> > >
> > > We would want the VHOST_RUN_WORKER calls to be infrequent to avoid the
> > > penalty of switching into the kernel, copying in the arguments, etc.
> >
> > I didn't get this part. Why have the timeout? When the timeout expires,
> > does userspace just call right back down to the kernel or does it do
> > some sort of processing/operation?
> >
> > You could have your worker function run from that ioctl wait for a
> > signal or a wake up call from the vhost_work/poll functions.
>
> An optional timeout argument is common in blocking interfaces like
> poll(2), recvmmsg(2), etc.
>
> Although something can send a signal to the thread instead,
> implementing that in an application is more awkward than passing a
> struct timespec.
>
> Compared to other blocking calls we don't expect
> ioctl(VHOST_RUN_WORKER) to return soon, so maybe the timeout will
> rarely be used and can be dropped from the interface.
>
> BTW the code I posted wasn't a carefully thought out proposal :). The
> details still need to be considered and I'm going to be offline for
> the next week so maybe someone else can think it through in the
> meantime.
One final thought before I'm offline for a week. If
ioctl(VHOST_RUN_WORKER) is specific to a single vhost device instance
then it's hard to support poll-mode (busy waiting) workers because
each device instance consumes a whole CPU. If we stick to an interface
where the kernel manages the worker threads then it's easier to share
workers between devices for polling.
I have CCed Stefano Garzarella, who is looking at similar designs for
vDPA software device implementations.
Stefan
next prev parent reply other threads:[~2020-11-20 8:46 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-12 23:18 [PATCH 00/10] vhost/qemu: thread per IO SCSI vq 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 ` [PATCH 00/10] vhost/qemu: thread per IO SCSI vq Stefan Hajnoczi
2020-11-17 19:13 ` 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 [this message]
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=CAJSP0QVu4P6c+kdFkhw1S_OEaj7B-eiDqFOVDxWAaSOcsAADrA@mail.gmail.com \
--to=stefanha@gmail.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=sgarzare@redhat.com \
--cc=stefanha@redhat.com \
--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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
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).