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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>
Subject: Re: [PATCH 00/10] vhost/qemu: thread per IO SCSI vq
Date: Thu, 19 Nov 2020 17:08:47 +0000
Message-ID: <CAJSP0QUfqd=QNFa-RikH4dVcLmfcP-pYCwznP3W0zobYkM+KDw@mail.gmail.com> (raw)
In-Reply-To: <ffd88f0c-981e-a102-4b08-f29d6b9a0f71@oracle.com>

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.

Stefan

  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 ` [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 [this message]
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

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