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

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Message-ID: <CACGkMEtw9eWGZ04gs0zKdnJks+AHQyKHWdqNdhCNBbiXsB9X+Q@mail.gmail.com>
Date:   Wed, 21 Dec 2022 11:19:56 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Yongji Xie <xieyongji@...edance.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 6:02 PM Yongji Xie <xieyongji@...edance.com> wrote:
>
> 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.

Right.

Thanks

>
> Thanks,
> Yongji
>