linux-kernel - Re: [PATCH v2 05/11] vduse: Introduce bound workqueue for irq injection

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Date:   Tue, 20 Dec 2022 18:01:51 +0800
From:   Yongji Xie <xieyongji@...edance.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Christoph Hellwig <hch@....de>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 05/11] vduse: Introduce bound workqueue for irq injection

On Tue, Dec 20, 2022 at 2:28 PM Jason Wang <jasowang@...hat.com> wrote:
>
> On Mon, Dec 19, 2022 at 1:04 PM Yongji Xie <xieyongji@...edance.com> wrote:
> >
> > On Fri, Dec 16, 2022 at 12:02 PM Jason Wang <jasowang@...hat.com> wrote:
> > >
> > > On Mon, Dec 5, 2022 at 4:44 PM Xie Yongji <xieyongji@...edance.com> wrote:
> > > >
> > > > This introduces a bound workqueue to support running
> > > > irq callback in a specified cpu.
> > > >
> > > > Signed-off-by: Xie Yongji <xieyongji@...edance.com>
> > > > ---
> > > >  drivers/vdpa/vdpa_user/vduse_dev.c | 29 ++++++++++++++++++++++-------
> > > >  1 file changed, 22 insertions(+), 7 deletions(-)
> > > >
> > > > diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > > index 37809bfcb7ef..d126f3e32a20 100644
> > > > --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> > > > +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > > @@ -57,6 +57,7 @@ struct vduse_virtqueue {
> > > >         struct vdpa_callback cb;
> > > >         struct work_struct inject;
> > > >         struct work_struct kick;
> > > > +       int irq_effective_cpu;
> > >
> > > I wonder why it's a cpu number instead of a cpumask. The latter seems
> > > more flexible, e.g when using NUMA.
> > >
> >
> > This variable represents the CPU that runs the interrupt callback
> > rather than CPU affinity.
>
> Ok, but for some reason it only gets updated when a new affinity is set?
>

Yes, since we don't use round-robin now. And if affinity is not set,
we rollback to the default behavior (use un-bounded workqueue to run
irq callback).

> (Btw, I don't see how the code deals with cpu hotplug, do we need
> cpuhot notifier?)
>

Currently the queue_work_on() can handle the cpu hotplug case, so I
think we can simply check whether the CPU is online each time queuing
the kwork, then update the affinity if needed.

Thanks,
Yongji